Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
411 AM AST Wed Jul 24 2024

.SYNOPSIS...
Hot temperatures will persist in the region through the period. A
very dense Saharan Air Layer is expected to persist from Thursday
through Saturday. A strong tropical wave could reach the islands
by next Wednesday.

&&

.SHORT TERM...Today through Friday...

Light passing showers continued to move across the region along the
ongoing trade wind flow. Minimal to no rainfall was observed over
land and this pattern will prevail into the morning hours. A robust
high across the Atlantic basin will remain in place throughout the
short term, maintaining breezy easterly lower level winds. Later
today the approach of a tropical wave in the eastern Caribbean will
bring an increase of showers during the afternoon hours, mainly
across western Puerto Rico. Isolated thunderstorms may bring minor
flooding across urban areas.

Following this increase of moisture, a slot of dry air will bring a
break in weather before some moisture being pushed by a dense
Saharan Air Layer arrives. A wind surge is expected with this second
band of moisture, which will increase the rate of showers during
Thursday morning into mid day. This wet pattern from this afternoon
to tomorrow will quickly end as the Saharan dust invades the region.
High dust concentrations are expected, reaching optical depth
above 0.6 at times, which is quite severe. We are expecting hazy
conditions into the weekend with poor visibilities. Also, hot
conditions are forecast each day with heat advisories likely for
mostly every coastal area.

.LONG TERM...Saturday through Wednesday...

A surface high pressure north of the islands will begin to migrate
toward the west, lifting most of the Saharan Air Layer with it. On
Saturday, skies will remain hazy, with elevated temperatures and a
low probability of precipitation. If showers managed to form, they
will be focused in the southwest of Puerto Rico. On Sunday and
Monday, an upper level trough located northeast of the islands
will induce weak perturbations that will be carried by the trade
winds into the region. This means an increase in shower activity,
over portions of the Virgin Islands and eastern Puerto Rico, with
stronger convection developing over western Puerto Rico in the
afternoon hours.

For the last couple of days of July, the weather will be variable,
with these small patches of moisture and small pockets of Saharan
dust. However, the most interesting feature would be a tropical
wave that should be close to the islands by Wednesday. The ECMWF
ensemble members show some tropical development associated with
this wave, while the GFS does not show any development at all. The
latest outlook from the Climate Prediction Center indicates that
there is a change greater than 20% of tropical cyclone
development, mentioning a more favorable atmosphere and the warm
sea surface temperatures. As it is usual with this kind of
forecast, uncertainty is very high at this point, and the forecast
will be adjusted with the latest guidance. The users are advised
to revisit their flooding and hurricane plans as we head into the
more active months of the season.


&&

.AVIATION...
(06Z TAFs)

Mainly VFR conditions expected to prevail through the
forecast period. SHRA will continue to move across the local waters,
but without significant impacts to operations. After 17Z, additional
SHRA expected to develop around TJSJ and TJBQ, with periods of
reduced VIS and low ceilings. Winds will be from the ESE at 17-22
kts, with stronger gusts.

&&

.MARINE...
Surface high-pressure spread across the Central Atlantic will
continue to support moderate to fresh easterly winds and choppy
seas for small crafts over the next few days. The proximity of an
upper trough and sufficient trade wind moisture transport will
promote shower and isolated thunderstorm activity across portions
of the coastal waters each day. A severe to extreme dust event will
bring hazy skies by Thursday into the weekend.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
419 AM AST Thu Jul 25 2024

.SYNOPSIS...
Passing showers today will be followed by a severe Saharan dust
event that will last into late Saturday. This air layer will
deteriorate air quality and will reduce visibilities. Variable
weather conditions are anticipated early in the weekend, but then,
a strong tropical wave is expected to arrive next Wednesday.


&&

.SHORT TERM...Today through Saturday...

A wind surge with some moist air moving across the region this
morning will bring some brief passing showers and gusty winds.
Nothing significant in terms of rainfall is expected with the this
band of moisture that arrives before the thick Saharan Air Layer
that will cause a rapid drying pattern overnight, lasting through
the short term. High concentrations of Saharan Dust calculating
Optimal Thickness values above 0.6 at times will invade the region
causing hot and hazy conditions through at least Saturday, with the
peak of the event expected on Saturday. Rainfall will be little to
non at this time, with the occasional little shower across windward
sections and possibly some light showers out west during the
afternoon. Best bet is to expect barely any to no rainfall as it
will be very dry and dusty.

Maximum temperatures are likely to rise in the 90s for coastal
regions, and express higher than normal values across higher
elevations during this time. At the moment, there is no heat
watch in effect, however be aware that it will be hot over the
next few days. This Saharan Dust Event is pretty severe, the worst
of the season and, climatologically speaking, only 5% of these
events reach this level.


.LONG TERM...Sunday through Thursday...

Significantly less Saharan dust is expected for next week.
However, skies will still look hazy at times. An upper level
trough well northeast of the Lesser Antilles will induce small
patches of moisture east of the region, and the trade winds will
drag these areas of clouds into to local islands. On Tuesday,
another layer of Saharan dust will arrive, limiting shower
activity for the western portions of Puerto Rico. Then, by
Wednesday and Thursday show a strong tropical wave reaching the
region. This wave should elevate the potential of flooding and
lightning at least to elevated. On the other hand, there should
be a relief from the scorching heat that has been punishing the
islands this summer. The solutions of the main global models
differ, however, so there is a lot of uncertainty in the forecast.
For now, the forecast lies on the wet side of the guidance, but
modifications will me made once the big picture becomes clearer.


&&

.AVIATION...
(06Z TAFs)

Mainly VFR conditions expected to prevail through the forecast
period. Passing showers and an increase of wind velocity is expected
this morning before the arrival of Saharan Dust this evening. East
winds at 17-22 kts, with stronger gusts and sea breeze variations.
Hazy conditions expected after 25/19z.

&&

.MARINE...
Surface high-pressure spread across the central Atlantic will
continue to support moderate to fresh easterly winds and choppy
seas for small crafts over the next few days. A tropical wave will
move south of the islands today, bringing passing showers to the
region. The wave will be followed by a severe Saharan dust event that
will last into late Saturday, resulting in hazy skies.

&&

.BEACH FORECAST...
Increasing winds will lead to areas of moderate rip current risk
for the next several days, mostly in southern and northern Puerto
Rico and for Saint Croix.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
449 AM AST Fri Jul 26 2024

.SYNOPSIS...

A strong Saharan Air Layer will remain in place for the next few
days, promoting hazy skies and limited shower activity across the
islands. Seasonal pattern will return from Sunday onwards with
patches of moisture carried by the trade winds. Breezy conditions
and an increase in showers are expected by midweek as a tropical
wave moves across the local area.


&&

.SHORT TERM...Today through Sunday...

A very dense Saharan Air Layer has entered the region this morning,
providing hazy and hot conditions for the days to follow with little
to no rainfall expected today and tomorrow. According to NASA
Goddard Earth Observing System Model V5, dust concentrations are
calculating Optimal Thickness values of around 0.6 over land which
is quite severe in terms of the strength for this event. This
appears to be the worst event of the season so far, and one of the
worst in the recent past. Hot days are expected as a result of this
airmass, allowing maximum temperatures and heat indices to reach
higher than normal values. Therefore, an excessive heat warning will
be in effect today for western coastal areas of Puerto Rico and an
advisory for all other coastal areas besides eastern PR, Culebra,
and Vieques. Today, light passing showers are possible across
windward sections and possible for western Puerto Rico during the
afternoon but only a very light shower, almost a drizzle is to be
expected.

Models are hinting at a better chance for rain across southwestern
Puerto Rico tomorrow under a east-northeast lower level wind flow,
however it seems unlikely due to the density of this Saharan air
mass that will suppress most rainfall. On Sunday, the arrival of
patches of moist air will begin to break the dry pattern. Expect an
increase of showers for eastern Puerto Rico and then more during the
afternoon for western Puerto Rico. A pretty seasonal pattern to be
expected this day, possibly with some lingering haze as the dusty
air mass moves out of the region to the west.


.LONG TERM...Monday through Friday...

TUTT induced perturbations in the trades will reach the islands
from the east on Monday and early Tuesday morning. This will
promote seasonal weather conditions across the islands, with
passing trade wind shower across the USVI and eastern sections of
PR during the night and early morning hours, and afternoon
thunderstorm development over the interior and western PR.
Increasing the risk for urban and small stream flooding. Later on
Tuesday, a weak SAL moves in and hazy skies and limited shower
activity should prevail.

For Wednesday and Thursday, guidance still suggest an increase in
moisture content and breezy trades between 20-25 knots as a
tropical wave streams across the northeastern Caribbean. The
precipitable water content increases between 2.00-2.25 inches
during this period. The risk for urban and small stream flooding
will increase in general across the islands. Lingering moisture on
Friday will enhance the diurnal convection, and at the same time
another Saharan Air Layer is forecast to reach the eastern
Caribbean.


&&

.AVIATION...
(06Z TAFs)

Hazy skies will limit visibilities across the local flying area
through the forecast period. VIS will remain from 5SM to 9SM. The
easterly winds will push quick passing -SHRA/SHRA from time to time.
Expect east-southeast winds at 15-20 kts, with stronger gusts and
sea breeze variations, and sightly diminishing after 26/21z.


&&

.MARINE...

Seas are expected to range between 2 and 5 feet across most
Atlantic and Caribbean waters today. However, seas between 4 and 6
feet are expected across the southern portions of the Mona
Passage. Small craft should exercise caution due to winds up to 20
knots by early this afternoon across most coastal and offshore
waters. Hazy skies will prevail due to a significant Saharan dust
event, this will decrease the visibility in general. East winds
will prevail but will acquire a northeasterly component on
Saturday.


&&

.BEACH FORECAST...

Increasing winds this afternoon will promote a moderate risk of rip
currents across most beaches of St. Croix, and the east and southern
coasts of Puerto Rico.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
513 AM AST Sat Jul 27 2024

.SYNOPSIS...

Hot and hazy skies due to a strong Saharan Air Layer will prevail
through at least the weekend. Shower and thunderstorm activity is
expected to increase by next week, particularly by mid-week as a
vigorous tropical wave approaches the area.

&&

.SHORT TERM...Today through Monday...

Hazy skies due to a strong Saharan Air Layer will prevail through at
least early Sunday. Hot temperatures are expected to continue today
with heat indices expected to range from 106 to 112 degrees
Fahrenheit, mainly along the lower elevations of western, southern
and northern Puerto Rico, and St. Croix. Therefore, a Heat Advisory
(NPWSJU) was issued across these areas, and could likely be issued
once again on Sunday and Monday as the SAL exits the region and
dewpoints increase. Although shower activity will be limited in
general, diurnally induced streamers developing off the USVI and
smaller islands and showers with possible isolated thunderstorms
could still develop during the afternoons over portions of
west/southwest PR.

On Monday, a TUTT induced trade wind perturbation or weak trough is
expected to move from the east and bring an increase in moisture
content. Precipitable water content could increase between 1.75-2.00
inches by Monday afternoon. Therefore, showers will increase in
coverage as well as the potential for better organized afternoon
convection over the interior and western Puerto Rico. Urban and
small stream flooding can be expected with this activity. Drier
conditions and hazy skies will follow quickly by Monday night as a
weak Saharan Air Layer filters from the east.

.LONG TERM...Tuesday through Saturday

A seasonal weather pattern will prevail on Tuesday, with slightly
below-normal to near-normal moisture levels across the forecast
area. This will bring occasional trade wind showers over windward
coastal areas during the morning hours and a few isolated
thunderstorms across western Puerto Rico.

Afterward, forecast details become more complicated as several
features will reach the northeastern Caribbean by mid-week.
Troughiness aloft will promote favorable weather conditions
conducive to convective development. At low levels, a wind surge
will first reach the local islands by early Wednesday, bringing
gusty wind conditions and squally weather to the region. From the
rest of the day through Thursday, a vigorous tropical wave behind
the wind surge will increase moisture content to well above normal
levels, in some instances reaching close to 2.40 inches. The
National Hurricane Center is currently monitoring the tropical wave
with a low formation chance in the next seven days. However,
uncertainty remains as some global models now predict the tropical
wave developing after it passes the CWA. The timing also differs
between models, with the ECMWF forecasting the tropical wave
arriving and exiting the region earlier than the GFS model.

Adding to this complex scenario is the presence of another Saharan
Air Layer event engulfing this tropical wave. The Saharan dust
particulates could be another limiting factor for shower and
thunderstorm activity. The rest of the week will depend on the
behavior of this tropical wave. The GFS model predicts lingering
moisture lasting through the weekend, potentially prolonging the wet
and unstable weather period.

Forecast confidence is low regarding the impact of this tropical
wave on the forecast area for next week. Therefore, continue to
monitor the forecast, as slight deviations in the tropical wave's
path and intensity could change the expected impacts across the
local islands. Regardless of the outcome, we can expect a shift in
weather conditions with increased instability and an elevated
flooding threat. This could potentially bring heavy rain, frequent
lightning, and gusty winds. Quick river rises and landslides
cannot be ruled out as this tropical wave crosses the northern
Caribbean.


&&

.AVIATION...
(06Z TAFs)

Mainly VFR conditions expected to prevail across all terminals thru
the next 24 hours. HZ due to Saharan dust may reduce visibilities
around 6SM through the forecast period. East to northeast winds
increasing at 15-20 kts, with stronger gusts and sea breeze
variations aft 27/14Z. -RA/VCSH expected early in the morning at
TJSJ/TJBQ, and btw 27/18z-22z at TJPS.


&&

.MARINE...

Surface high-pressure located in the central Atlantic will continue
to support moderate to locally fresh easterly winds and choppy seas
for small crafts over the next few days. A strong Saharan dust event
will continue to affect the local islands at least until early
Sunday, resulting in hazy skies and limiting shower activity.
By mid-week of next week, a vigorous tropical wave will promote
shower and thunderstorm activity across the regional waters along
with hazardous seas.

&&

.BEACH FORECAST...

Increasing winds this weekend into early next week will promote
moderate risk of rip currents for north- and east-facing beaches.
A vigorous tropical wave will reach the local islands by mid-week
of next week. This will increase shower and thunderstorm activity
across the area. Gusty wind conditions could increase rip current
risk to high in some beaches as well.

[cycloneye]

National Weather Service San Juan PR
430 AM AST Mon Jul 29 2024

.SYNOPSIS...
The Saharan Air Layer that affected the region in previous days
has dissipated and moved off with a much cleaner and somewhat drier
airmass in place. However, hot and humid conditions will persist
today through Tuesday, followed by an increasing moist and unstable
weather pattern by Wednesday with the arrival of a vigorous tropical
wave which is forecast to bring increasing moisture content across
the region. Consequently there will be increased potential for enhanced
shower and thunderstorm activity. The National Hurricane Center continues
to watch this wave and area of disturbed weather as it continues westward
across the central tropical Atlantic. Please continue to monitor the
forecast and latest Tropical Weather Outlook (TWOAT) as this possible
event unfolds.

&&

.SHORT TERM...Today through Wednesday

Variably cloudy skies due to tradewind showers prevailed across
the eastern sections of Puerto Rico and the smaller islands during
the overnight hours. The Doppler radar estimated up to a quarter
of an inch of rain with some of these showers. Minimum temperatures
ranged from the upper 60s and lower 70s in the higher mountain
valleys to the low 80s across coastal areas. These tradewind
showers will persist through the rest of the morning, causing
slippery roads and ponding of water on roadways and in poor
drainage areas.

Warmer-than-usual conditions will persist today. Consequently, most
urban and coastal areas will experience a limited to elevated excessive
heat threat, increasing the possibility of heat exhaustion with prolonged
exposure. Therefore, Heat Advisories have been issued for the northern,
western, and southern coastal areas of Puerto Rico and St. Croix.

A trade wind perturbation will stream across the forecast area
today. GOES-16 Satellite imagery shows an area with high moisture
content just northeast of the northern Leeward Islands. This
perturbation is expected to reach the local area by late this
morning into early afternoon. Precipitable water content will reach
2.0 inches or slightly higher for the rest of the day. High low-
level moisture content, in combination with intense surface heating
and local effects, will promote convective activity this afternoon,
particularly across western interior and northwestern Puerto Rico.
On Tuesday, slightly drier conditions in combination with another
weak pulse of Saharan Air Layer will decrease the frequency of
shower activity bringing back hazy skies, although for a short
period of time. Nevertheless, enough low-level moisture with surface
heating could promote convective activity during the afternoon hours
across western Puerto Rico. This convective activity will be shallow
for the most part, but a few isolated thunderstorms cannot be ruled
out.

For the rest of the short-term forecast, weather conditions will
transition to a more unstable and wet pattern. Model guidance
suggests the arrival of a wind surge on Wednesday, which could bring
squally weather, promoting gusty wind conditions and frequent
lightning across the area. Dynamics aloft will turn favorable as
some troughiness settles over the region, with 250 mb heights
dropping and prevailing cold air advection at upper levels. Models
suggest increasing lapse rates with 500 mb temperatures continuously
cooling for the rest of the week. This will further enhance the
potential for organized convection as it interacts with the wind
surge.

Furthermore, behind this wind surge, we continue to expect the
approach of a vigorous tropical wave that the National Hurricane
Center is monitoring, now with a 0% and 50% probability of
developing into a tropical cyclone in the next two and seven days,
respectively. Although some uncertainty is still present with this
tropical wave, its moisture field is very broad, which could
interact with instability aloft. Therefore, an increased flooding
risk is expected, with the potential for quick river rises, landslides,
and possible flash flooding in some areas. Please stay tuned for
further updates as we continue to analyze the expected weather
conditions this week.

.LONG TERM...Thursday through Monday

The latest tropical outlook from the National Hurricane Center
puts the tropical wave at a medium chance (50%) of developing into
a tropical cyclone in the next seven days. However, the recent model
guidance that do develop it suggests that it should do so after passing
our region. The EURO model ensembles still shows development occurring
just north or northwest of Puerto Rico, while the Canadian CMC model
develops it over the Caribbean waters, well southwest of the forecast
area. The GFS ensembles suggests much less potential for development
and continues to suggest a strong tropical wave with broad moisture
field. This expected broad moisture field associated with the wave
so far appears to be accompanied by and wrapped up in a good plume
of Saharan dust. This in fact may be one of the limiting factors
in how much this waves develops and how soon. However sea surface
temperatures and environmental conditions are forecast to remain
conducive for some development by Thursday.

Regardless of development, we should remain alert and prepare for a
wetter and unstable weather pattern through Thursday or early Friday
with moisture content expected to be well above normal. Several
variables continue to suggest favorable conditions aloft, such as
decreasing 250 MB heights with erosion of the upper ridge, cooler
advective 500 MB temperatures, and steeper low- to mid- level lapse
rates which all suggest unstable conditions. If this all unfolds,
the combination of instability with plenty of tropical moisture
will enhance convective development with possibly strong thunderstorms
and thus increasing the potential for flash flooding during that
time. Additionally,both the ECMWF and GFS Galvez- Davison Index
products continue to suggest the potential for isolated to scattered
thunderstorms, capable of producing periods of heavy rainfall with
the most impactful period being late Wednesday through Thursday.

Overall confidence is still low as there remains uncertainty as to
how much the aforementioned feature will develop before it reaches
the northeastern Caribbean, as well as the exact path that this wave
will take. This will therefore ultimately dictate its potential impacts
for the forecast region. Please continue to monitor the latest forecast
and Tropical weather outlook and keep in mind that weather conditions
may shift to a more unstable and wet pattern at least through Thursday
or early Friday.

The forecast for the latter part of the period, will depend on the how
much lingering moisture will trail the aforementioned tropical wave.
Recent model guidance remain persistent in maintaining marginal instability
through Friday due to troughiness in the mid to upper levels and sufficient
available moisture. Therefore, with available moisture, and good heating
expect active afternoons each day, particularly over the Cordillera
Central and western Puerto Rico. Some developing streamers will be
possible downwind of the U.S. Virgin Islands and mountainous areas
such as El Yunque. This expected afternoon convection will be steered
by the dominant easterly low level flow. For this reason, the flood
risk will remain elevated throughout the long- term forecast.

&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, trade wind showers may cause
brief MVFR cigs across TJSJ/TJBQ and the USVI terminals during the
morning hours. VCTS/TSRA expected at TJBQ due to afternoon TSRA
developing over the Cordillera, with VCTS at times at TJPS/TJSJ.
East winds expected at 12-16 kt with higher gusts and sea breeze
variations aft 29/14z.

&&

.MARINE...

The interaction of the surface high-pressure across the central
Atlantic and a low-pressure over Central America will continue to
tighten the local pressure gradient. This will favor moderate to
fresh easterly winds and choppy seas for the next several days.
Periods of passing showers will continue over the local waters and
passages, with a chance of isolated thunderstorms especially off
the west coast of Puerto Rico during the afternoon hours. By Wednesday,
a vigorous tropical wave being observed by the National Hurricane
Center is forecast reach the regional waters and bring an increase
in shower and thunderstorm activity along with hazardous seas and
possibly squally conditions.

&&

.BEACH FORECAST...

Low rip current risk will prevail today for all the local beaches.
Increasing winds will promote moderate rip current risk throughout
the week and breezy conditions along the local beaches.

[cycloneye]

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
431 AM AST Tue Jul 30 2024

.SYNOPSIS...
Quick passing tradewind showers will continue to affect the regional
waters and portions of the islands during the rest of the early morning
hours. A drier airmass is expected to filter in later today with only
a light concentration of Saharan dust expected to linger. A wet and
unstable pattern is forecast to unfold from Wednesday and through
the rest of the workweek due to the arrival of a vigorous tropical
wave forecast to cross the region through Thursday with trailing
moisture expected thereafter. The National Hurricane Center continues
to monitor this elongated wave as it moves across the tropical Atlantic
and approaches the Lesser Antilles. Please continue to monitor the
forecast and latest Tropical Weather Outlook (TWOAT) for further
updates.

&&

.SHORT TERM...Today through Thursday

Similar weather conditions to the previous night were observed
during the morning hours, with variably cloudy skies due to trade
wind showers across windward coastal areas. The Doppler radar
estimated up to half an inch of rain, though localized 1-inch
rainfall was also detected in the Naguabo municipality as a strong
patch moved through the area. GOES-16 satellite imagery indicates a
slightly drier slot east of the forecast area gradually filtering
in. Precipitable water values will drop to at least 1.6 inches,
remaining slightly below to near climatological normal. Thus, the
frequency of showers should diminish through the morning hours.
Nonetheless, sufficient low-level moisture will combine with diurnal
heating and local effects, once again supporting another round of
shower and thunderstorm activity in the afternoon. This activity
should cluster in similar areas where high rainfall accumulations
were observed the previous day, though with less areal coverage.

Tonight will start relatively calm as additional drier air moves in
due to an area of subsidence ahead of a wind surge. Precipitable
water values, along with 850-700 mb and 700-500 mb levels, will drop
to below climatological normal levels before rapidly increasing as
the wind surge approaches late tonight and early Wednesday. For the
rest of the short-term forecast, moisture content will remain well
above normal across the CWA, with dynamics aloft becoming more
favorable for thunderstorm activity. As mentioned in previous
discussions, there is a tropical wave behind the wind surge that
will bring very wet conditions as it interacts with a series of
retrogressing TUTTs north of the area.

The National Hurricane Center (NHC) has been monitoring this
disturbance for quite some time. According to the latest Tropical
Weather Outlook (TWO), this wave now has a 0% and 60% probability of
tropical cyclone development in the next two and seven days,
respectively. However, the NHC has moved the potential development
area downstream of the forecast area. This trend is seen in several
model solutions, particularly from the ECMWF, with a vigorous
tropical wave approaching the area. Uncertainty persists regarding
the amount of rainfall expected from this wave. The ECMWF QPF
Extreme Forecast Index has consistently indicated that the area with
the highest likelihood of extreme precipitation will stay mostly
north of Puerto Rico. Nevertheless, both the GFS and ECMWF have been
consistent in indicating the potential for isolated to scattered
thunderstorms over the region due to the presence of high moisture
content and instability across the forecast region.

To sum up, by early Wednesday, squally weather can be expected as
the wind surge crosses the area. Shower and thunderstorm activity
will move from the eastern half of the CWA to interior and western
Puerto Rico in the afternoon. An east-northeast steering wind flow
will cluster most of the activity across western and southwestern
Puerto Rico. The axis of the tropical wave will start to cross the
forecast area by Wednesday night into early Thursday, with the
steering wind flow shifting to a more southeasterly direction and
trailing moisture for the rest of the week. We can expect alternating
periods of gusty wind conditions, frequent lightning, and heavy showers,
with relatively calmer weather as these two weather features cross
the region. Some areas will be impacted more than others, particularly
in regions with previous rainfall activity and currently elevated
streamflows. Landslides and flash flooding events cannot be ruled
out during this period. For this reason, stay tuned for any advisories
or warnings that our office may issue in the coming days.

.LONG TERM...Friday through Tuesday...

As previously mentioned, the recent Tropical Weather Outlook from
the National Hurricane Center continued to put the area of disturbed
weather and elongated tropical wave at a near zero percent chance
for tropical cyclone formation during the short term and a medium
chance (60%) of developing into a tropical cyclone in the next seven
days. Although there continues to be some inconsistencies in the long
term model guidance, they do however suggest some development after
the tropical wave passes the region north or northwest of the forecast
area. Both the EURO and GFS models continued to suggest a significant
increase in tropical moisture accompanying and trailing the strong
tropical wave. Recent satellite imagery and aerosol products continued
to suggests that this moisture field is accompanied by and being wrapped
up in a dry Saharan air layer as it approaches the region. Consequently,
this will be one of the limiting factors in how and if this waves develops.
However, the above normal sea surface temperatures and expected environmental
conditions are forecast to later become conducive for some development
later in the period.

Regardless of further development of this wave, we still expect a fairly
moist and unstable weather pattern through Friday and now possibly into
the weekend, due to trailing moisture advection, low level speed convergence
and good daytime heating. Several variables continue to suggest somewhat
favorable conditions aloft at least through Friday or early Saturday,as
there is some erosion of the mid to upper level ridge along with cooler
advective 500 MB temperatures. Thereafter the upper level ridge builds
across the region once again and moisture quickly erodes while the Atlantic
surface ridge builds north of the region and local pressure gradient
tightens. This scenario will all promote increasing tradewinds with
breezy to windy conditions by late Saturday and through the rest
of the long term period.

Light to moderate concentrations of Saharan dust will continue to
move in and out of the region during the period along with weakly
induced easterly pertubations which will bring occasional patches
of trade wind moisture and showers to the islands and coastal waters
during the overnight and early morning hours. In addition, there will
be sufficient moisture availability each day for afternoon convection
combined with good daytime heating and the hot and humid conditions.
The afternoon shower development should be focused over the Cordillera
Central and western Puerto Rico, but with the expected increasing
winds over the weekend, developing streamers will be possible downwind
of the U.S. Virgin Islands and over mountainous areas such as El Yunque,
resulting in some showers possible in and around parts of the SanJuan
metro steered by the dominant easterly low level flow. For this reason,
the flood risk will remain elevated for isolated areas mainly in Puerto
Rico at least through the early part of the long- term forecast.

&&

.AVIATION...
(06z)

VFR conditions will prevail. Isold-SHRA in a streamer off of El
Yunque are psbl aft 30/15Z, with psbly brief MVFR/IFR conds at TJSJ.
SHRA with isold TSTMS will dvlp aft 30/17Z in wrn PR and along the
west half of the Cordillera Central. TSRA in the vcnty of TJBQ/TJPS
are psbl. East southeast winds will increase to 12 to 18 knots arnd
30/14Z with sea breeze variations at all sites.

&&

.MARINE...The pressure gradient over the region will continue to
tighten across the region favoring moderate to fresh easterly winds
and choppy seas for the next several days. Small craft operators
should exercise caution especially over the offshore waters and
local passages. A vigorous tropical wave being monitored by the
National Hurricane Center is forecast reach the regional waters by
Wednesday bringing an increase in shower and thunderstorm activity
along with hazardous seas and possibly squally conditions.

&&

.BEACH FORECAST...
Low rip current risk will prevail today for most of the local
beaches except for Cramer park beach in St Croix where there will
be a moderate risk. Increasing winds by Wednesday will promote
moderate rip current risk for the rest of the period for most
beaches with breezy conditions forecast along local beaches.

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
510 AM AST Thu Aug 1 2024

.SYNOPSIS...

A unstable and wet pattern will persist today as the tropical
wave moves west-northwestward across portions of the Greater
Antilles. Today, there is a moderate to high potential of showers
and thunderstorms across the region. Therefore, the risk of
flooding is elevated to significant. Weather conditions are
expected to improve by the weekend with the entrance of a drier
airmass and slight concentrations of Saharan Dust.

&&

.SHORT TERM...Today through Saturday...

A robust tropical wave produced widespread shower and thunderstorm
activity across Puerto Rico and its surrounding waters, while the
U.S. Virgin Islands did not receive significant rain activity.
Showers and thunderstorms affected most of PR overnight, with the
maximum rainfall accumulations observed across the east, the San
Juan Metropolitan area, and the south coast from Coamo to Guanica.
The unstable and wet weather promotes nighttime cooling along the
coastal and the low-elevation regions, where the minimum temperature
finally dropped into the mid and upper 70s. Along the mountain
areas, the lows were in the upper 60s. Winds were mainly from the
east to east-southeast at 10 knots or less, but windy (20-30 mph)
gusty winds were estimated near and around thunderstorms.

The unstable and wet pattern will persist today as the tropical wave
moves west-northwestward across portions of the Greater Antilles.
For today, we expect favorable environmental conditions for the
development of thunderstorms across the surrounding waters. The
steering wind flow will dominate from the southeast, giving a
moderate (40-50% chance) to a high chance (60-80% chance) of
thunderstorms and showers moving across PR's south and east coast,
crossing the islands. Therefore, we expect showery and stormy
weather today, and you may experience strong thunderstorms producing
frequent lightning, strong gusty winds, and flooding, especially
during the morning and afternoon hours. Please exercise caution,
especially in flood-prone areas.

Although we can anticipate periods of calm weather with no rain from
time to time, the unstable and wet pattern associated with the
moisture field of the tropical wave will maintain a moderate to high
chance of seeing showers and thunderstorms each day through at least
Saturday. The above-normal sea surface temperatures around the
islands may promote nighttime showers and thunderstorms each night,
especially late tonight into early Friday morning. The risk of
flooding will be elevated to significant, especially as soils
continue to saturate and the river's streamflow runs above normal.

On Saturday, the trailing tropical wave moisture will promote
scattered-to-numerous overnight and morning passing showers across
the windward sections. Then, the sea breeze, excessive heating, and
local effects will enhance the afternoon convection across the
mountains and downwind from them. The summer muggy heat index will
also persist, especially across areas where rain does not affect
them.

.LONG TERM...Sunday through Thursday...

Relatively calmer weather conditions will dominate the long-term
period compared with the past week. An easterly perturbation is
expected to move across the area by the weekend along with light
to moderate concentrations of Saharan Air Layer. Patches of
tradewind moisture will come along too, promoting the enhancement
of shower activity over portions of the islands. This activity
will be more focused over the western and northwestern portions of
Puerto Rico due to the combination of southeasterly winds,
diurnal heating and local effects. In addition, the San Juan
streamer could bring showers into the San Juan metro area and
adjacent municipalities. Across the U.S. Virgin Islands, fair
weather conditions will dominate as well, with little or none
precipitation over the islands.

A continuation of the dry weather pattern is expected by mid-week,
with the presence of a strong high pressure in the central
Atlantic and the approach of another pulse of Saharan Air Layer.
In response to the surface high pressure, the potential for heavy
showers and thunderstorms will remain limited. However, a strong
thunderstorm cannot be ruled out across the interior and western
Puerto Rico during the afternoon hours.

Warm temperatures will continue to prevail. With highs in the upper
80s to low 90s along the urban and coastal areas, and in the mid 80s
elsewhere. Heat indices could reach over the 108 degrees Fahrenheit
at times, leading to Heat Advisories or Excessive Heat Warning.
Moving into the tropics, at this moment the latest model guidances
(GFS & ECMWF) are not suggesting tropical development for the
local area during the period. Nonetheless, please continue to
monitor the Tropical Weather Outlooks (TWO) provided by the NWS
National Hurricane Center (NHC) as we move into the peak of the
Hurricane Season.

&&

.AVIATION...
(06Z TAFS)

Expect SHRA/TSRA across the local terminals throughout the fcst
period. Therefore, MVFR to brief IFR conditions are possible at any
given time for all terminals (especially across JSJ/JPS this morning
and afternoon, and at JBQ during the afternoon). However, VFR
conditions will be observed at times. Mtn top obscd and low cigs
expected along the Cordillera Central thru 01/23z. Calm to light and
VRB winds thru 01/13z. Then winds will be mainly from the ESE/SE at
10-20 kt with higher gusty winds due to sea breeze and near TSRA.

&&

.MARINE...

A broad tropical wave will continue to cross the local area through
today. This wave will continue to bring showers and thunderstorms
along with locally higher seas and squally weather conditions across
the regional waters and local passages through the end of the
workweek. Increasing easterly winds will become moderate to fresh
creating choppy to occasionally rough seas late in the workweek and
into the weekend.

&&

.BEACH FORECAST...

There is a moderate risk of life-threatening rip currents along
the northern and eastern beaches of Puerto Rico, including
Culebra and St. Croix.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
531 AM AST Fri Aug 2 2024

.SYNOPSIS...

Trailing moisture associated to a distant tropical wave will
continue to develop showers and thunderstorms today across the
region. This activity will generate frequent lightning, strong
gusty winds, and flooding. Any additional showers in the morning
and afternoon hours could lead to flooding, quick river rises,
and mudslides. A gradual improvement will be observed by the
weekend with the arrival of a much drier airmass into the region.

&&

.SHORT TERM...Today through Sunday...

The moisture field from yesterday's tropical wave led to another
active night across the surrounding waters, the eastern third of
Puerto Rico, and the northern US Virgin Islands. Doppler Radar
estimated rainfall accumulations between 1 and 2 inches. The
strongest thunderstorms were observed across the Caribbean and
Atlantic Local waters once again overnight. The unstable and wet
weather promoted nighttime cooling along the coastal and the low-
elevation regions, with minimum temperatures in the mid and upper
70s. In the mountain areas, the lows were in the upper 60s. Winds
were mainly from the east-southeast at 10 knots or less, but windy
(20-30 mph) gusty winds were estimated near and around
thunderstorms.

The moisture field trailing yesterday's tropical wave will create
conducive environmental conditions for the development of
thunderstorms across the local islands and surrounding waters. The
east-southeast steering wind flow will pool an area with above-
normal moisture over the USVI and PR, estimated by GOES-E Total
Precipitable Water from 2.10 to 2.33 inches. This concentration of
moisture will lead to a moderate (40-50% chance) to a high chance
(60-80% chance) of thunderstorms and showers moving across south,
east, and northeast PR and USVI throughout the morning, spreading
into the rest of mainland PR from mid-morning onward. The resulting
weather will be showery and stormy, with the potential for strong
thunderstorms producing frequent lightning, strong gusty winds, and
flooding, especially during the morning and afternoon hours. Given
the saturated soils and high river stream flows from yesterday's
rain, the risk of river flooding and mudslides is heightened with
persistent heavy rain today. Caution is advised, especially in flood-
prone and mudslide-prone areas.

On Saturday, the trailing tropical wave moisture will promote
scattered-to-numerous overnight and morning passing showers across
the windward sections. Then, the sea breeze, excessive heating, and
local effects will enhance the afternoon convection across the
mountains and downwind from them. The summer muggy heat index will
also persist, especially across areas where rain does not affect
them. A similar weather pattern will prevail on Sunday but with less
frequency and coverage in rain activity. Additionally, the dangerous
heat index values may return on Sunday due to the combination of the
above-normal moisture content and the maximum air temperatures.


.LONG TERM...Monday through Friday...

A strong surface high pressure located over the central Atlantic
will promote easterly tradewinds through the long-term period. A
wind surge is expected to move relatively fast over the local
islands by late Sunday into early Monday, leaving minor rainfall
accumulations over the area. After the wind surge moves, patches
of moisture will continue to arrive into the area promoting
showers and isolated thunderstorms, mainly during the afternoon
hours over western Puerto Rico.

A drier airmass is expected to filter into the region by
Wednesday, with precipitable water content values between 1.55 to
1.70 inches. Light concentrations of Saharan Air Layer are also
possible. Therefore, hazy skies and limited shower activity is
anticipated over the region. However, due to the combination of
daytime heating and local effects, afternoon convective activity
will be observed each day across the interior and western
portions of Puerto Rico.

Across the U.S. Virgin Islands the week looks relatively calmer.
Tradewind passing showers may affect the islands during the morning
hours, with minimal precipitation anticipated. Temperatures
across the islands will remain warm to hot. Highs will be in the
upper 80s to low 90s along the coastal and urban areas, and in the
mid 80s along the higher elevations. Heat indices may reach the
108 degrees Fahrenheit leading to Heat Advisories and/or Excessive
Heat Warning.

At this moment, tropical development is not expected across the
Atlantic basin or the northeastern Caribbean. Please continue to
monitor the Tropical Weather Outlooks (TWO) provided by the NWS
National Hurricane Center (NHC) as we move into the peak of the
Hurricane Season.

&&

.AVIATION...
(06Z TAFS)

Expect SHRA/TSRA across the local terminals throughout the fcst
period. Therefore, MVFR to brief IFR conditions are possible at any
given time for all terminals (especially across JSJ/JPS this morning
and afternoon, and at JBQ/IST/ISX/JSJ during the afternoon). Mtn top
obscd and low cigs expected along the Cordillera Central thru
02/23z. Calm to light and VRB winds thru 02/13z. Then winds will be
mainly from the ESE/SE at 10-20 kt with higher gusty winds due to
sea breeze and near TSRA.

&&

.MARINE...

The departing tropical wave will continue to bring additional
showers and thunderstorms along with locally higher seas and squally
weather conditions today. Moderate to fresh easterly winds will
generate choppy to occasionally rough seas into the weekend.

&&

.BEACH FORECAST...

The moderate risk of life-threatening rip currents along the
northern and eastern beaches of Puerto Rico, including Culebra and
St. Croix will prevail through the weekend.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
505 AM AST Sat Aug 3 2024

.SYNOPSIS...

Hot and humid conditions across the urban and coastal areas will
lead to dangerous heat levels that can affect people's health.
Local effects will result in afternoon showers and thunderstorms,
mainly across the interior and western PR. Ahead of Sunday
afternoon wind surge, a Saharan Air Layer will limit rain
activity, resulting in hazy skies. A TUTT-low will sink southward
from the North Atlantic, retrogressing across the Northeast
Caribbean early next week, around Tuesday and Wednesday. A
tropical wave will move northwestward from the southeast Caribbean
into the region around mid-week. Trade wind perturbations will
arrive Thursday and Friday, followed by another tropical wave next
Saturday.

&&

.SHORT TERM...Today through Monday...

Relatively calm conditions were observed during the overnight hours
under clear to partly cloudy skies. Few trade wind showers
reached the eastern portions of Puerto Rico and the U.S. Virgin
Islands, leaving minimal accumulations. Minimum temperatures were
observed from the upper 60s and lower 70s in the higher elevations
to the upper 70s to low 80s across coastal and urban areas. Winds
were mainly from the east at 10 knots or less.

Today, trailing moisture from Tropical Depression Four (now located
south of Cuba) in combination with diurnal heating, local effects,
and see breeze will enhance the potential for shower and
thunderstorm activity. This activity is mainly expected over the
central interior and western portions of Puerto Rico. The latest
precipitable water content guidance suggest values of 1.80 to 1.90
inches. Urban and small stream flooding are possible across these
sectors with the heaviest rains. A patch of drier air will quickly
follow early this evening, along with light to moderate
concentrations of Saharan Air Layer. These particles will promote
hazy skies through Sunday evening.

On Sunday, similar weather conditions are expected with the arrival
of a wind surge. This event will move over the local islands
promoting wet and unstable weather through Monday.

Warmer-to-hot conditions will persist through the rest of the period
with limited to elevated excessive heat threat. Maximum temperatures
could reach the upper 80s to low 90s along the coastal and urban
portions of the islands to the mid 80s in the higher elevations.
Heat indices will be hot today, that may lead to dangerous heat
levels that can affect people health. Therefore, a Heat Advisory
and a Excessive Heat Warning will be in effect for the coastal and
urban areas of Puerto Rico and the U.S. Virgin Islands.

.LONG TERM...Tuesday through Saturday

High humidity and maximum air temperature will result in muggy
heat indices on Tuesday and may extend the period with warm and
hot apparent temperatures. However, a TUTT-low will sink southward
from the North Atlantic, retrogressing across the Northeast
Caribbean early next week, around Tuesday and Wednesday,
increasing the instability, which, combined with sea breeze
variations, the traces of the suspended Saharan Dust particles and
excessive heating will result in strong afternoon convection,
each day. The above-normal sea surface temperatures will also
promote nighttime convection across the regional waters that may
move inland across the windward portions of PR and the USVI.

A more unstable and wet pattern may evolve around mid-week with
the arrival of a tropical wave. Although the typical summer
weather pattern will prevail on Thursday and Friday, a set of
trade wind perturbations could sometimes bring showery and stormy
weather. Another possible strong tropical wave may form, arriving
near the region by next Saturday. Puerto Rico and the U.S. Virgin
Islands residents and visitors are encouraged to monitor the
tropical weather as we move into the peak of the Atlantic
Hurricane Season.

&&

.AVIATION...

(06Z TAFS)

Mainly VFR conds are expected across all terminals throughout the
forecast period. Tradewind showers will result in VCSH at TIST/TISX
aft 03/13z. However, an increase in afternoon SHRA/TSRA is expected
across western Puerto Rico and may result in brief MVFR conds at
TJBQ aft 03/17Z. Mtn top obscd and low cigs expected along the
Cordillera Central thru 03/22-23Z. Light and VRB winds thru 03/13z.
Winds will prevail from the ESE at 10-20 kt with higher gusts
through 03/23Z.

&&

.MARINE...

Moderate to fresh easterly winds will generate choppy to
occasionally rough seas into early next week. Showers with isolated
thunderstorms will likely affect the local waters, particularly the
coastal waters of western Puerto Rico and local passages each
afternoon. A tropical wave will move across the eastern Caribbean
around Tuesday.

&&

.BEACH FORECAST...

Beachgoers, the waters across the Atlantic will have northeasterly
wind waves between 3 and 5 feet, with occasional seas up to 6 feet
and a wave period of around 8 seconds. Meanwhile, the Caribbean
wind waves will range between 2 and 4 feet with occasional seas up
to 5 feet, a wave direction from the southeast, and a wave period
of around 5 seconds. The rip current risk will be moderate for the
PR's Atlantic Coastline and St Croix.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
502 AM AST Sun Aug 4 2024

.SYNOPSIS...

Despite today's wind surges and increase in showery activity, we
anticipate another day of intense heat and humidity in the urban
and coastal areas, posing potential health risks due to dangerous
heat levels. Additionally, a Saharan Air Layer will contribute to
hazy skies in the region through the middle of the week. A TUTT-
low from the North Atlantic will sink southward, brushing the
Northeast Caribbean by Tuesday and Wednesday. Meanwhile, a
tropical wave will move northwestward from the eastern Caribbean
into our region between Tuesday and Wednesday. Trade wind
perturbations will impact us on Thursday and Friday before another
tropical wave arrives over the weekend, separated by an air mass
with suspended Saharan Dust Particles.

&&

.SHORT TERM...Sunday through Tuesday...

Overnight, mainly calm weather conditions were observed across the
islands. Tradewind showers reached portions of the U.S. Virgin
Islands and eastern Puerto Rico, leaving rainfall accumulations of
less than 0.10 inches. Minimum temperatures were observed in the mid
to upper 60s and lower 70s in the higher mountain elevations to the
upper 70s to low 80s along the coastal areas. Winds prevailed mainly
from the east at 10 kts or less.

A wind surge is expected to cross the local region today, increasing
moisture and shower activity over the islands. As a result, the
combination of moisture, sea breeze, diurnal heating and local
effects will result in showers and thunderstorms during the
afternoon over interior to western Puerto Rico. Urban and small
stream flooding are possible across these sectors with the heaviest
rains. The metropolitan area of San Juan may observe the development
of the El Yunque streamer, resulting in showers and isolated
thunderstorms in the afternoon. Easterly winds steered by a strong
high pressure in the central Atlantic will prevail through the rest
of the period. In addition, moderate concentration of a Saharan Air
Layer will persist, promoting hazy skies through mid-week.

The unstable trend will continue through much of the workweek. On
Tuesday, a TUTT-low will sink southward from the North Atlantic
increasing the instability across the northeast Caribbean region.
Expect strong active afternoon convection over the interior and
western portions of Puerto Rico. For the rest of the area, hot and
humid conditions will persist through the week.

Hot conditions will continue with elevated to significant excessive
heat threat. Maximum temperatures could reach the upper 80s to low
90s along the coastal and urban portions of the islands to the mid
80s in the higher mountain elevations. Heat indices will be hot
today, once again. These conditions may lead to dangerous heat
levels that can affect people health. Therefore, a Heat Advisory and
a Excessive Heat Warning will be in effect for the coastal and urban
areas of Puerto Rico and the U.S. Virgin Islands.

.LONG TERM...Wednesday through Saturday

The days with muggy heat indices will persist on Wednesday.
However, a TUTT-low brushing the Greater Antilles will increase
instability aloft to interact with a tropical wave, which,
combined with sea breeze variations, the traces of the suspended
Saharan Dust particles and excessive heating will result in strong
afternoon convection, especially during the afternoon and evening
hours. The overnight convection will be enhanced by the above-
normal sea surface temperatures across the regional waters, and it
may move inland across the windward portions of PR and the USVI.

The typical summer weather pattern will prevail on Thursday and
Friday, with trade wind perturbations bringing additional moisture
and instability that could result in occasional showery and
stormy weather. The "NASA Dust Extinction Aerosol Optical
Thickness" guidance suggests an area with significant suspended
African desert dust particles before the arrival of another
tropical wave next weekend. Then, another tropical wave will move
near the region of Puerto Rico and the U.S. Virgin Islands by next
weekend.


&&

.AVIATION...
(06Z TAFS)

Mainly VFR conds expected to prevail across all terminals through
the forecast period. Tradewind showers will result in VCSH at
TJSJ/TIST/TISX thru 04/13Z. Today, a wind surge is expected to cross
the islands. Therefore, and increase in afternoon SHRA/TSRA may
result in brief MVFR conds at TJSJ/TJBQ aft 04/17Z. Mtn top obscd
and low cigs expected along the Cordillera Central thru 04/22Z.
Light to moderate winds thru 04/13z. East winds at 15-20 kt with
higher gusts and sea breeze variations through 04/22Z.

&&

.MARINE...

A wind surge will bring a slight increase in shower activity
today, especially in the afternoon, when thunderstorms may form
across western PR, moving into the Mona Passage and downwind from
the U.S. Virgin Islands.

Moderate to fresh easterly winds will generate choppy to occasionally
rough seas into early next week. Showers with isolated thunderstorms
will likely affect the local waters, particularly the coastal waters
of western Puerto Rico and local passages each afternoon. A tropical
wave is expected to move across the eastern Caribbean region by
Tuesday.

&&

.BEACH FORECAST...

Beachgoers, the waters across the Atlantic will have northeasterly
wind waves between 3 and 5 feet, with occasional seas up to 6 feet
and a wave period of around 7 seconds. Meanwhile, the Caribbean
wind waves will range between 2 and 4 feet with occasional seas up
to 5 feet, a wave direction from the southeast, and a wave period
of around 5-6 seconds. The rip current risk will be moderate for
the PR's Atlantic Coastline and St Croix. The moderate risk of rip
currents will spreads across most of the coastal areas in PR and
St Croix today.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
425 AM AST Mon Aug 5 2024

.SYNOPSIS...

Some Saharan Dust particles will contribute to hazy skies across the
region through the middle of the week. A TUTT-low from the North
Atlantic will sink southward by Tuesday and Wednesday while a
tropical wave will move across the Caribbean waters Tuesday through
Wednesday. Trade wind perturbations will impact us on Thursday and
Friday before another tropical wave arrives over the weekend,
separated by an air mass with suspended Saharan Dust particulates.
Hot and humid conditions will likely persist through the week.
Therefore excessive heat conditions can be expected especially along
the coastal and urban areas.

&&

.SHORT TERM...Today through Wednesday...

Overall calm conditions prevailed in most areas during the overnight
and morning hours across Puerto Rico and the U.S. Virgin Islands.
However, some showers moved across the coastal waters and reached
the east and southeastern PR as well as the metro area. During the
afternoon, showers will be focused over the interior and west to
southwestern PR. Low temperatures were in the low 80s along the
coastal areas and in the upper 60s to low 7s in higher elevations
and valleys. Additional passing showers are expected across the
local waters and eastern Puerto Rico during the rest of the early
morning. Winds were from the east northeast 10 mph or less but will
increase to 12 to 18 mph with higher gust during the rest of the
day. In addition, some suspended Saharan Dust particulates present
across the forecast area will promote hazy skies through mid-week.

The most recent satellite-derived precipitable water imagery shows
that moisture levels continue to decrease across the area. A Saharan
Air Layer will continue to spread across the region, resulting in
hazy skies. However, this particulates are not too dense, so
visibilities are not expected to be greatly reduced. A mid to upper
level trough will dig from the south from today into Wednesday,
although the area that it is more favorable for the development of
showers and thunderstorms should remain away from the region. At the
same time, a well defined tropical wave is forecast to move south of
the region on Tuesday, but the most of the moisture field should
remain over the Caribbean waters, without reaching Puerto Rico or
the Virgin islands. Additionally, a broad surface high pressure
centered well to the north of the islands will maintain the gradient
tight, resulting in breezy conditions, with wind speeds generally
from the east and up to as much as 20 mph with occasionally
higher gusts during the daytime.

Taking all of these factors into consideration, only a few passing
showers are expected to develop across the local waters, reaching
the U.S. Virgin Islands and eastern Puerto Rico at times. Strong
diurnal heating will also lead to thunderstorms in the interior and
west in the afternoon hours. Conditions are not favorable for
significant rainfall accumulation, but ponding of water on roadways
and low-elevated areas will be possible. The day with the highest
probability of precipitation is late Tuesday and Wednesday, and it
will remained focus across the eastern interior during the overnight
and morning hours and central interior and western Puerto Rico
during the afternoon hours.

In terms of temperatures, the above normal Sea Surface Temperatures
surrounding the islands will lead to the continuation of maximum and
minimum temperatures still above normal, as well as for the heat
indices. This heat will likely affect people without effective
cooling or adequate hydration.

&&

.LONG TERM...Thursday through Sunday

The inherited forecast remains on track. We anticipate the typical
summer pattern prevailing on Thursday, with mostly calm weather
and some shower activity over the western quadrant of Puerto Rico
by the afternoon. The "NASA Dust Extinction Aerosol Optical
Thickness" guidance suggests an area with suspended Saharan dust
particles with values ranging around 0.20, meaning that this could
be a slight to moderate dust event. However, the latest model
guidance shows an easterly perturbation reaching Puerto Rico and
the U.S. Virgin Islands by late Friday into Saturday. This feature
will bring additional moisture and instability, which could
result in occasional showers and stormy weather. A tropical wave
is forecast to approach the forecast area by the beginning of the
workweek.

&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions expected to prevail. HZ due to
Saharan dust is expected, but with no significant impact to
operations. Winds will be from east from the SFC to 14,000 feet,
at 16-25 kts. VCSH are expected in the vicinity of the USVI
terminals for the period, with more significant activity after 17Z
for the Cordillera Central. Mountain obscuration is possible from
17-22Z.

&&

.MARINE...

Moderate to fresh easterly winds will generate choppy to occasionally
rough seas today. Showers with isolated thunderstorms will likely
affect the local waters, particularly the coastal waters of western
Puerto Rico and local passages each afternoon. A tropical wave is
expected to move across the eastern Caribbean region by Tuesday and
Wednesday, with locally higher seas expected for the offshore
Caribbean and Mona Passage.

&&

.BEACH FORECAST...

There is a high risk of rip currents for northeastern and eastern
Puerto Rico, as well as Saint Croix through at least Tuesday.
The risk is moderate to low for the remaining coastal areas of Puerto
Rico, Vieques, Culebra, and St Thomas.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
514 AM AST Sat Aug 10 2024

.SYNOPSIS...

Warm-to-hot conditions are expected to persist through early next
week, with Heat Advisories in effect today. A series of tropical
waves and associated wind surges will impact the region through
early next week, maintaining elevated risks for excessive
rainfall, non-thunderstorm winds, and marine and rip current
hazards. A strong tropical wave with a high chance of developing
into a tropical cyclone will likely approach the northeastern
Caribbean by Tuesday into Wednesday. Residents and visitors are
urged to stay vigilant and review their tropical emergency plans
during this period.


&&

.SHORT TERM...Today through Monday

During the overnight hours, calm conditions have persisted over most
of the islands, however, showers have continued over the local
waters. Some showers moved inland, especially over eastern and
northern PR, Vieques, Culebra, and the USVI. Overnight minimum
temperatures were observed in the upper 70s to lower 80s across
coastal areas of the metro area, northeastern, and southwestern
Puerto Rico. In higher elevations, temperatures dropped to the upper
60s to mid-70s.

A surface high-pressure system over the tropical Atlantic will move
more towards the central Atlantic, while a TUTT will continue to
approach from the northeast during the short-term period. A tropical
wave near the area is increasing showers across the waters. At this
time, the latest Precipitable Water (PWAT) models suggest values
around normal climatological levels, around 1.8 to 1.9. Moisture
levels are expected to gradually increase today through the forecast
period as additional induced perturbations and patches of moisture
will continue to reach the area with a wind surge. For today,
showers will continue particularly across the eastern sectors and
USVI during the morning. Then, there is a high chance of showers
with isolated thunderstorms developing across the interior and
western Puerto Rico during the afternoon hours, mainly because of
the combination of sea breeze variations and excessive diurnal
heating. Despite the expected rains, due to the anticipated
dangerously hot and humid conditions today, an Excessive Heat
Advisory has been issued for northern and western Puerto Rico.
Overall, expect warm to hot conditions to continue through Monday
and showers with isolated thunderstorms each day, supporting
excessive rainfall risks throughout the period mainly across eastern
PR during the mornings, and then across the interior and western PR
during the afternoons.

.LONG TERM...Tuesday through Friday...

Long-term forecast hazards are centered on potential impacts from
a tropical wave that the National Hurricane Center is monitoring
for possible tropical cyclone development over the next seven
days. According to the NHC's projected formation area and the
latest model guidance, this system is expected to move generally
west to west-northwestward and could approach the northeastern
Caribbean by early mid-week. Regardless of whether it develops
into a tropical cyclone, the current forecast for Puerto Rico and
the Virgin Islands suggests a significant deterioration in weather
conditions starting as early as Tuesday afternoon and lasting
through early Thursday morning, raising concerns about flooding.
Weather conditions are expected to improve quickly later in the
week as a drier-than-normal air mass, with pockets of low-level
moisture, moves in.

In the latest Tropical Weather Outlook, the NHC has maintained a
high formation chance (80 percent) for this system, indicating it
will likely become a tropical depression by early to mid-next week
as it approaches and moves near or over the Lesser Antilles. Due
to uncertainties in its development, it is too early to determine
the potential tropical cyclone-related impacts this system may
bring to Puerto Rico and the Virgin Islands, such as winds or
storm surges. However, we strongly encourage the public to stay
alert and monitor official updates on this system. Use this time
to review your tropical emergency plan, including preparing an
evacuation strategy, assembling disaster supplies, creating a
communication plan, and securing your home.


&&

.AVIATION...
(06Z TAFS)

VFR conditions across all TAF sites should dominate through the
forecast period. However, brief MVFR conditions are possible with
the development of SHRA/TSRA between 08/16-22Z over the interior to
western PR. VCSH have and VCTS have been added to most sites.
Easterly winds should increase to 10-20 knots with higher gusts and
sea breeze variations after 08/14Z.

&&

.MARINE...

A series of tropical waves and associated wind surges will move
through the eastern Caribbean region into early next week. These
systems will bring increased showers, isolated thunderstorms, and
moderate to fresh winds, maintaining choppy to hazardous marine
conditions for small craft. For this reason, a Small Craft
Advisory is in effect for the offshore Atlantic waters through
this afternoon. Further deterioration in marine and weather
conditions is expected by midweek with the arrival of another
tropical wave that has a high chance of developing into a tropical
cyclone. Refer to the Marine Weather Message (MWWSJU) for more
information.


&&

.BEACH FORECAST...

Today, there is a moderate risk of rip currents at most local
beaches. This risk is expected to increase to a high level by
Tuesday. For more information, please refer to the Coastal Hazard
Message (CFWSJU) and Surf Zone Forecast (SRFSJU).

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
515 AM AST Wed Aug 14 2024

.SYNOPSIS...

A Tropical Storm Warning remains in effect for Puerto Rico and
the U.S. Virgin Islands through this evening. Tropical Storm
Ernesto is bringing strong gusty winds and heavy rainfall to the
region. A significant risk of flooding remains expected, with
mudslides likely in areas of steep terrain. Marine and coastal
conditions will remain deteriorated today. A gradual improvement
in weather conditions is expected by tonight as Ernesto moves
further north of the region and over the open Atlantic waters.

&&

.SHORT TERM...Today through Friday...

A Tropical Storm Warning remains in effect for Puerto Rico and
the U.S. Virgin Islands. At 500 AM AST (0900 UTC), the center of
Tropical Storm Ernesto was located near latitude 19.5 North,
longitude 66.6 West, moving toward the northwest at 16 mph (26
km/h). The center is currently about 85 miles north- northwest of
San Juan with strong and frequent rainbands affecting most of the
area. Tropical storm sustained winds are expected across most of
the eastern side of Puerto Rico, Culebra, Vieques and the U.S.
Virgin Islands this morning. Lingering moisture will persist this
afternoon providing conditions for ongoing rainfall. Marine and
coastal conditions will remain deteriorated with seas greater than
10 feet and life- threatening rip currents, and rough surf
conditions lasting through at least late this afternoon.

Ernesto is expected to produce total rain accumulations of 4 to 6
inches over the U.S and British Virgin Islands. Rainfall totals
of 6 to 8 inches, with maximum amounts of 10 inches, are expected
across southeastern Puerto Rico, with totals of 2 to 4 inches
across northwestern Puerto Rico. Flooding remains a threat were
flash flooding and mud/landslides are possible. A gradual
improvement in weather conditions is expected by tonight. By
Thursday, warm and hot conditions will return along with fair
weather across the region.

Residents and visitors should continue to monitor the progress of
this system and have their tropical emergency plans ready now.
Please refer to the latest Tropical Cyclone Bulletin (TCPAT5) issued
by National Hurricane Center and Hurricane Local Statements (HLSSJU)
issued by WFO San Juan PR for updated information.

&&

.LONG TERM...Saturday through Tuesday...


The current forecast track has Tropical Storm Ernesto far away
from our region by Friday, about 650 miles, and it is forecast to
be a Hurricane at that time. Weather conditions should improve in
our local area and return to a more typical pattern. The latest
Precipitable Water (PWAT) models suggest values returning to
average values. The interaction of surface winds across the
Atlantic due to Ernesto's positions and a surface high pressure
across the eastern Atlantic should promote southeasterly winds
through Sunday, then shift from the east on Monday lasting through
Tuesday. At the upper levels, a TUTT will approach from the
northeast, promoting favorable conditions aloft for daily showers.

In general, local weather during the long term will be dominated
by east-to- southeast winds, daytime heating, and local effects.
Therefore, afternoon convective activity with showers and
thunderstorms is expected across the interior and northwestern
Puerto Rico. For the U.S. Virgin Islands, passing showers dragged
by the winds will reach the islands mainly during the morning
hours. Limited excessive rainfall risk will probably be present as
ponding of water in roads and poorly drained areas is possible
with shower activity, mainly on Friday. Warm conditions will
return by Friday and last through the weekend, mainly across
coastal and lower elevations.

&&

.AVIATION...
(06Z TAFS)

SHRA/TSRA associated to the rainbands from TS Ernesto will continue
to affect the region, generating MVFR to brief LIFT conditions
throughout the period. W winds in TJSJ and TJPS and N winds in TJBQ
at 15-30 knots will gradually turn from the WSW-ESE at 15-20 knots
after 14/14Z. Winds at US terminals will remain from the S at 30-40
knots, decreasing to 20-30 knots after 14/14Z. SHRA/TSRA will
decrease once Ernesto moves away.

&&

.MARINE...

Tropical Storm Ernesto, located 85 miles north- northwest of
San Juan, will continue to move northwestward across the Atlantic
waters, exiting the area later today. Rough, hazardous seas will
continue at through at least tonight. Conditions are expected to
improve on Thursday.

&&

.BEACH FORECAST...

Beach conditions will continue deteriorate as Tropical Storm
Ernesto moves through the region. Large breaking waves are
expected to impact the Virgin Islands and Puerto Rico today
through tonight. High Surf Advisory and High Rip Current
Statements are in effect through at least tonight.

&&

HYDROLOGY...

Tropical Storm Ernesto will bring rainfall accumulation of 4 to 8
inches with maximum amounts of 10 inches for portions of the
Virgin Islands, eastern and southern Puerto Rico, as well as the
interior. The risk of flooding will be significant, with rapid
river rises, and mudslides likely. Please refer to the latest
Flash Flood Watch (FFWSJU) for additional information.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
440 AM AST Fri Aug 16 2024

.SYNOPSIS...

Excessive heat hazards will be present today and during the next
few days. There is a chance for afternoon showers and
thunderstorms to develop each day, even during the driest periods,
with increased frequency and intensity during the weekend and
during the second half of the next workweek as tropical waves
affect the region at those times. Pulses of Saharan dust will
continue to reach the region. River flood warnings are in effect
for the Culebrinas and Guanajibo rivers at least through early
this morning.

A moderate rip current risk will return tonight and persist
through most of the weekend for several areas. A high risk of rip
currents is forecast for some areas by Sunday night and into
early next week as swells from Hurricane Ernesto and moderate to
locally fresh winds impact the local waters, also creating choppy
seas for small craft by Sunday into early next week.

&&

.SHORT TERM...Today through Sunday...

Satellite imagery and doppler weather radar depicted partly cloudy
to variably cloudy skies overnight, with a mix of high level clouds
spilling over the region from distant Hurricane Ernesto and patches
of low to mid level clouds and few showers moving across the region
while brushing parts of the islands. So far rainfall accumulations
were little to none with these light passing showers. Rivers and
streams along the northern half of Puerto Rico continued slightly
higher than normal but were slowly declining to near normal.
However, in the west section of Puerto Rico ,Both Culebrinas and the
Hormigueros river remained at high level overnight although steadily
subsiding but with flood waters still remaining over some major
roadways, making hazardous conditions for residents and drivers. For
this reason a Flood warning remains in effect at least later this
morning. The early morning low temperatures were in the low 80s
along the coastal areas and in the mid to upper 70s in higher
elevations. Daytime highs today will range between 89 to low 90
degrees, with maximum heat indices expected to soar once again into
the lower 110s over portions of the islands where Excessive Heat
Warnings and advisories will be likely. Winds were calm to light and
variable but will become from the east southeast 10 to 15 mph with
sea breeze variations and occasionally higher gust during the
afternoon hours.

For the rest of the short-term period, a much drier airmass is
expected at least into early Friday with winds becoming in more east
northeast in advance of a weak tropical wave and mid to upper level
trough expected to approach and cross the region from the east by
Saturday afternoon through early Sunday. So far expect most of the
moisture with this wave to pass south of the region, however some
peripheral moisture may converge across the region bringing
intervals of passing clouds and showers to the region. Recent model
guidance and satellite derived Layered precipitable water products
both suggest a drier airmass with values dropping to between 1.35
and 1.65 inches at least until early Saturday, along with a low to
moderate concentration of Saharan dust to linger across the region
through the period. Expect generally fair weather skies but still 40-
60% chance for afternoon showers with isolated thunderstorms over
northwestern Puerto Rico, driven by significant diurnal heating and
sea-breeze convergence. By Saturday afternoon, more favorable
conditions are expected due to the nearby mid-to-upper level trough
and increasing PWAT values nearing 2.0 inches as the tropical wave
cross the eastern Caribbean and approaches just south of the region.
This will likely aid in increasing the potential for showers and
isolated thunderstorms, with up to a 70% chance of precipitation by
Saturday afternoon and into early Sunday. The forecast then calls
for a limited to elevated risk of excessive rainfall and lightning
hazards for Saturday through early Sunday. Thereafter by Sunday
afternoon onwards, more typical weather conditions are forecast with
east to southeast winds and diminishing moisture content once again.

Overall warmer-than-normal conditions will persist in the coming
days. and coastal and urban areas can expect nighttime lows in the
lower 80s, while higher elevations will see temperatures drop to
around low to mid 70s. Daytime highs will range from the upper 80s
to lower 90s in lower elevations to around 80 degrees in higher
elevations. Maximum Heat indices in many coastal and urban regions
may soar above 108 degrees Fahrenheit. These conditions will present
significant health risks and may require the issuance of Excessive
Heat Advisories and/or Warnings. It is crucial for residents and
visitors, especially those participating in outdoor activities, to
take necessary precautions to stay safe.

.LONG TERM...Monday through Friday...

No major changes to the long term forecast. Model guidance
indicates precipitable water (PWAT) values decreasing to below
normal and normal values to start the workweek, coinciding with a
pulse of saharan dust that will also serve to promote hazy skies.
PWAT values are forecast to further decrease on Tuesday before
gradually increasing to above normal values (above 2 inches)
through the second half of the workweek. This last increase will
be due to a tropical wave that, in addition to increasing
moisture, will increase the potential for enhanced shower activity
across the area. Surface high pressure across the Atlantic will
spread westward on Monday as Ernesto moves farther north. This
will promote more east to east-northeast winds through midweek,
becoming more easterly by the second half of the workweek. Heat
risks will persist through the workweek in addition to a generally
typical weather pattern. This pattern will include periods of
passing overnight and early morning showers across windward
sectors of the islands (especially windward sectors of Puerto
Rico), followed by afternoon showers and thunderstorms mainly
over the interior to western Puerto Rico each day. This activity
will be somewhat enhanced, Wednesday onwards.

&&

.AVIATION...

(06Z TAFs)

VFR conds at all terminals thru prd. Few passing SHRA ovr regional
waters and en route btw islands. Some -SHRA reaching windward side
of islands but no sig impacts to flight VIS. Low level steering wnds
generally fm ESE 5-15 kts BLO FL120. Sfc wnds calm to light and
variable bcmg fm east to northeast 10-15 kts aft 16/14Z with sea
breeze variations and hir gusts from time to time durg aftn. he
north coast today but some will appear aft 16/15Z. SHRA activity
with chc of isold TSRA in NW and interior PR btw 16/17-16/22Z.

&&

.MARINE...

Hurricane Ernesto, currently around 640 miles north- northwest of
San Juan, will continue to generate moderate southeasterly winds
despite its distance. Easterly winds are expected to return over the
weekend. Swells from Ernesto and moderate to locally fresh winds from
a tropical wave will create choppy seas for small craft early next
week.

&&

.BEACH FORECAST...

The rip current risk will remain low for all beaches during the
day. However, a moderate risk will return tonight for northwestern
to north-central Puerto Rico. The moderate risk will spread to
other areas during the weekend. A high risk of rip currents is
forecast for some areas by Sunday night and into early next week
as swells from Hurricane Ernesto and moderate to locally fresh
winds from a tropical wave impact the local waters.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
429 AM AST Sat Aug 17 2024

.SYNOPSIS...
Hot conditions will linger across the islands for the next several
days. A tropical wave will approach too, increasing the chances
of showers and thunderstorms. Saharan dust will follow this wave,
resulting in hazy skies.

&&

.SHORT TERM...Today through Monday...

Current Satellite derived precipitable water (PWAT) indicate a mass
of above normal values (above 2.0 inches) now over
easternmost/southeasternmost Puerto Rico, the USVI, Vieques and
Culebra. This contrasts the normal PWAT values (around 1.60 inches)
across the rest of the region. Passing showers slowly gained more
frequency overnight, affecting the eastern region of the area. One
particular isolated thunderstorm moved over St. Croix overnight.
Lows ranged from the upper 70s to the low 80s across lower
elevations of the islands to upper 60s and low 70s across interior
Puerto Rico.

We'll start the weekend with increasing moisture and instability as
a weak tropical wave affects the region today and tomorrow. Above
normal PWAT levels (above 2.0 inches) will be persist through late
Sunday. These conditions will give an extra boost to the typical
weather pattern. This pattern includes periods of passing overnight
and early morning showers across windward sectors of the islands,
followed by afternoon showers and thunderstorms mainly over interior
to western/northwestern Puerto Rico each day. Lines of convection
can also develop northwest of the local islands and El Yunque under
southeasterly winds. Winds will gradually back through the period,
becoming easterly on Monday. PWAT values will decrease to more
normal values to start the workweek, coinciding with a pulse of
saharan dust that will also promote hazy skies.

Elevated to significant heat risks will persist through the short
term period. For today (10 AM to 5 PM AST), an Excessive Heat
Warning will be in effect for all coastal and lower elevation areas
of the island, and a Heat Advisory will be in effect for lower
elevations (mostly the valleys of Caguas and Gurabo) of eastern
interior Puerto Rico. Drink plenty of fluids, stay in an air-
conditioned room (if possible and if power is available), stay out
of the sun, check up on relatives and neighbors, and take extra
precautions when outside. Conditions during the coming days present
significant health risks and may require the issuance of additional
Excessive Heat Advisories and Warnings.

.LONG TERM...Tuesday through Saturday

Hazy skies are anticipated on Tuesday as Saharan dust lingers. By
Wednesday, patches of moisture associated with a tropical wave
will approach. However, this system looks weak and rather
fragmented, so the shower activity should not be too widespread.
Additionally, the air mass will remain dry at the mid and upper
levels, so these showers should not have enough vertical
development to drop heavy rainfall accumulations. By the latter
part of the week, moisture will increase, and an upper level
trough will approach from the Lesser Antilles. In fact,
precipitable water value will be well above normal Thursday and
Friday. These days, showers will become more frequent over the
Virgin Islands and eastern Puerto Rico. The activity will be
stronger in the afternoon for the interior and western Puerto
Rico, where the risk of lightning and flooding will be elevated.

Hot temperatures will continue too. Temperatures at 925 mb will
not be as high as the past couple of days, but still above normal.
This heat will impact sensitive groups, especially those without
effective cooling or adequate hydration.


&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions across the terminals. S-SE winds up to 12 kts
with sea breeze variations and higher gusts, decreasing after
17/22Z, when land breezes start to influence. Brief MVFR conditions
can result from morning VCSH/VCTS that can affect eastern sites &
VCSH/VCTS starting over the interior that can affect the PR sites,
especially TJBQ around 17/17Z-22Z.

&&

.MARINE...
Light to moderate east-to-southeast winds will continue through the
weekend, providing favorable conditions for small craft. However,
moderate to locally fresh winds from a tropical wave will lead to
choppy seas for small craft early next week.

&&

.BEACH FORECAST...
The risk of rip currents is moderate today across the northern
coast of Puerto Rico. A swell from Hurricane Ernesto will reach
the islands by Monday, and the risk might increase to high.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
510 PM AST Sun Aug 18 2024

.SYNOPSIS...
Drier air associated with a Saharan Air Layer will arrive
overnight, continuing a dry trend for the beginning of the week.
This will also bring hazy and hot conditions that will last
through early Tuesday when the Saharan air layer moves out of the
area. The arrival of northerly swell from Hurricane Ernesto will
bring breaking waves around 6 to 7 feet for northerly Puerto Rico,
causing a high risk of rip currents for tomorrow.

&&


.SHORT TERM...Tonight through Tuesday...

A dry afternoon was seen across the islands with isolated
thunderstorms affecting the northwestern quadrant of Puerto Rico,
however only leaving less than an inch in Moca and Quebradillas.
Overnight the arrival of drier air associated with a Saharan Air
Layer will bring hot and hazy conditions for Monday through
Tuesday morning. Passing windward showers and afternoon convection
still remain possible during this time. Lines of convection can
also develop off the local islands and El Yunque. Surface winds
will gradually back through the period, becoming easterly (and
increasing) on Monday, and becoming more east- northeasterly on
Tuesday. Heat risks will persist through the short term period for
lower elevation areas, especially from late morning to late
afternoon. On Tuesday, there should be a rapid improvement in
visibility during the morning hours with the exit of the Saharan
Air Layer, being followed by a hot day with a typical weather
pattern of passing showers and afternoon thunderstorms out west.


&&


.LONG TERM...Wednesday through Sunday...
/from previous discussion/

An upper level low, with a reflection at the low levels will
travel westward across the Atlantic ocean, reaching Puerto Rico
and the Virgin Islands on Wednesday. The areas of moisture will
be fragmented, however, with some Saharan dust also trapped in the
circulation. The patches of moisture will be drive by a surface
high pressure northeast of the islands. This will also keep the
gradient tight, with speeds of 15 to 20 knots. On Wednesday, the
winds will be from the northeast, then switching from the east on
Thursday and Friday as the trough moves through. In general,
moisture levels will be near normal, or just above normal, with
intermittent patches of drier air reaching the islands. All this
ingredients will combine to result in a pattern of passing showers
reaching the Virgin Islands and eastern Puerto Rico throughout the
day, and with thunderstorms developing for the interior and west
in the afternoon hours.

Temperatures will stay in the warm side, just above normal, but
925 mb temperatures will be lower than in the previous days, so it
will be a tad more tolerable.


&&

.PREV DISCUSSION... /issued 1142 AM AST Sun Aug 18 2024/

LONG TERM...Wednesday through Sunday...

An upper level low, with a reflection at the low levels will
travel westward across the Atlantic ocean, reaching Puerto Rico
and the Virgin Islands on Wednesday. The areas of moisture will
be fragmented, however, with some Saharan dust also trapped in the
circulation. The patches of moisture will be drive by a surface
high pressure northeast of the islands. This will also keep the
gradient tight, with speeds of 15 to 20 knots. On Wednesday, the
winds will be from the northeast, then switching from the east on
Thursday and Friday as the trough moves through. In general,
moisture levels will be near normal, or just above normal, with
intermittent patches of drier air reaching the islands. All this
ingredients will combine to result in a pattern of passing showers
reaching the Virgin Islands and eastern Puerto Rico throughout the
day, and with thunderstorms developing for the interior and west
in the afternoon hours.

Temperatures will stay in the warm side, just above normal, but
925 mb temperatures will be lower than in the previous days, so it
will be a tad more tolerable.


&&

.AVIATION...
(18Z TAFs)

Mainly VFR conditions. SE winds up to 13 kts with sea breeze
variations and higher gusts, decreasing after 18/22Z. Brief MVFR
conditions due to VCSH/VCTS NW PR, especially VCTY TJBQ til 18/21Z.
Saharan dust will increase after 18/14Z for TIST/TISX and after
18/21Z for PR sites; Visibility P6SM. Winds will diminish ovr land
to less than 6 kts in mostly land breezes aft 18/22Z. SHRA with mtn
obscurations will return to ern PR aft 19/09Z.

&&

.MARINE...

Light to moderate east-to-southeast winds will continue through the
weekend, providing favorable conditions for small craft. However,
locally fresh winds will lead to choppy seas early in the week. The
arrival of a northerly swell from Hurricane Ernesto will raise seas
across the Atlantic water this evening through Monday.

&&

.BEACH FORECAST...

An arriving northerly swell produced by Hurricane Ernesto will
arrive this evening, providing a High Risk of Rip Currents for
tomorrow for northern Puerto Rico stretching from the beaches in
Rincon to Fajardo, also Culebra. Expect breaking waves around 6
to 7 feet for northern facing coastlines.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
439 AM AST Tue Aug 20 2024

.SYNOPSIS...

Another warm day is forecast across the coastal and urban areas
of Puerto Rico and the U.S. Virgin Islands. Therefore, a heat
Advisory is in effect from 10 AM to 5 PM AST today for the
northern and western coastal areas of Puerto Rico, including
Culebra, Vieques, and the U.S. Virgin Islands. By Thursday, a
tropical wave will move across the region, increasing the
frequency of the showers.

&&

.SHORT TERM...Today through Thursday...

The night was fairly tranquil with little rainfall activity. Some
showers did move over the local waters, but skies remained mostly
clear. Temperatures were on the warm side for coastal areas, with
lows in the low and mid 80s, and a little cooler along the mountain.
A surface high pressure and an approaching tropical wave will shift
the wind from the east to northeast today. Some Saharan dust lingers
today, so skies will look hazy at times. This air mass is also drier
than normal, with the recent satellite-derived precipitable water
imagery showing values around 1.4-1.5 inches (below normal). At the
mid levels, a ridge is also maintaining a dry air mass, so strong
rainfall activity should be limited to a small section of west-
southwest Puerto Rico this afternoon.

Then, as the tropical wave advances, columnar moisture will
increase, and showers and isolated thunderstorms will become more
frequent. The high resolution and global models show this activity
mainly moving across eastern Puerto Rico and the Virgin Islands in
the morning hours, followed by more showers and thunderstorm for the
Cordillera Central and western Puerto Rico in the afternoon hours.
This rain could be heavy at times, leading to urban and small stream
flooding, while rapid river rises and mudslides cannot be ruled out.
Conditions are not expected to change too much on Thursday. However,
the wind flow will turn from the east-southeast, so the focus of the
rain in the afternoon will shift to the northwest.

Temperatures will remain on the warm side today, but 925mb
temperatures show indications of temperatures a tad cooler later in
the week, likely related to the increase in rainfall and the cloud
coverage.

.LONG TERM...Friday through Tuesday...

The long-term forecast remains on track. From Friday into Monday,
plenty of tropical moisture will continue to reach the islands at
the surface under the east-southeast wind flow generated by a
broad surface of high pressure extending across the central into
the western Atlantic. At the mid to upper levels, an established
ridge is forecast to provide stable conditions aloft and a trade
wind cap inversion across the islands during the period. Under
this evolving pattern, the islands are forecast to observe the
typical summer weather pattern across the region with explosive
afternoon showers in the afternoon hours. The strongest showers
can be accompanied by isolated to scattered thunderstorms, as
suggested in the latest run for the Galvez-Davison Index (GDI),
especially for Saturday.

Global model guidance continues to suggest an increase in the
available moisture once again after a drier airmass slot moves
out of the region by late Monday into Tuesday. For now, the bulk
of the moisture will remain mostly in the south of the region,
just over the Caribbean waters, but it will be enough to enhance
shower development across the islands. Temperature-wise, the
islands will be experiment maximums around the upper 80s to the
lower 90s with heat indices near 105-112 degrees Fahrenheit.

&&

.AVIATION...
(06Z TAFS) Mainly VFR conditions expected to prevail trough the
forecast period. Isolated SHRA are moving across the local waters,
but no impacts are expected to operations. Stronger SHRA and TSRA
expected for the western Cordillera after 17Z, but the main activity
should stay away from TJPS or TJBQ. SHRA will also increase after
22z for TJSJ and TIST, and limited impacts to operations are
possible. Winds are from the east at 15 to 19 kts.

&&

.MARINE...
A building surface high pressure across the Atlantic will continue
to promote moderate to fresh easterly winds across the regional
waters today and tomorrow. Additionally, a weak northerly swell
from the very distant hurricane Ernesto will linger across the
Atlantic waters and Caribbean Passages, fading during the day.
Seas will remain from 3 to 5 feet with easterly winds up to 15
knots and gusty winds near the shower activity.

There is a moderate risk of rip Currents across most of the
exposed local coastal areas in Puerto Rico and the U.S. Virgin
Islands

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
428 AM AST Wed Aug 21 2024

.SYNOPSIS...

A tropical wave moving near the region will continue to result in
frequent passing showers across the region at least until
Thursday. Therefore, there will be an an elevated flood threat for
some areas with the afternoon convection. Moderate to fresh
easterly winds will result in choppy marine conditions, therefore
small craft operators should exercise caution.

&&

.SHORT TERM...Today through Friday...

Showers and isolated thunderstorms were observed during the night,
crossing the Virgin Islands, eastern and northern Puerto Rico.
Strong gusty winds were observed as well, and rainfall accumulations
reached a third of an inch across northern Puerto Rico. As the
tropical wave advances, moisture will continue to increase, and so
will the shower and thunderstorm activity. The winds are strong, out
of the east-northeast at 15 to 20 kts, and stronger gusts. This
strong wind flow will cause the showers to move quickly, but areas
that received rain after rain will likely experience some minor
urban flooding. In the afternoon, the activity will increase, and
the wave will spread into the Cordillera Central and western Puerto
Rico. The rain should be heavy at times too, with more minor
flooding impact anticipated.

Once the wave moves through today, the wind flow will shift from the
southeast, and the pressure gradient will remain tight. The air mass
will gradually dry out at the mid levels, but enough moisture will
linger, with above normal precipitable water values expected.
Therefore, another day with unsettled weather is in store. More
showers will move from the Caribbean Sea into the Virgin Islands and
east/southeast Puerto Rico. In the afternoon, the focus of rain will
be shifted to the northwest, but with such strong winds,
accumulations will likely stay in the 1 to 2 inches range.

On Friday, the winds shift again from the northeast, in response to
a stretching surface high pressure over the central Atlantic. The
mid levels will continue to dry, with slight concentrations of
Saharan dust too. Even with the drier air mass, local effect will
aid in the development of showers in the southwestern quadrant of
Puerto Rico.

With the increase in showers and thunderstorms on Wednesday and
Thursday, temperatures should be a tad cooler than previous days. In
fact, 925 mb temperatures will be near normal. Temperatures will
likely rise again by Friday, with lesser amounts of clouds in the
forecast.

.LONG TERM...Saturday through Wednesday...

The long-term forecast remains on track. Global model guidance
continues to suggest a stable weather pattern in the mid- to upper
levels provided by a mid-to-upper level ridge resulting in a
trade wind cap inversion and drier air aloft. Although conditions
would be mostly favorable for suppressing widespread shower
activity, trapped moisture in the lower levels will reach the
local islands, increasing the potential for afternoon showers.
Under this evolving pattern, the islands are forecast to observe
the typical summer weather pattern across the region, with
explosive afternoon showers in the afternoon hours across the
western and northwestern sections of Puerto Rico. The strongest
showers can be accompanied by isolated to scattered thunderstorms,
as suggested in the latest run for the Galvez-Davison Index
(GDI), especially for Sunday.

From Monday into Tuesday, the GFS and ECMWF global model guidance
continues to suggest an increase in the available moisture once
again after a drier airmass slot moves out of the region. For now,
the bulk of the moisture will remain mostly in the south of the
region, just over the Caribbean waters, but it will be enough to
enhance shower development across the islands. Temperature-wise,
the islands will be experiment maximums around the upper 80s to
the lower 90s with heat indices near 105-112 degrees Fahrenheit.

By Wednesday, the chances for widespread shower activity will
increase as a tropical wave moves across the region. Therefore,
the forecast calls for a medium to high probability of an increase
in the frequency of shower activity.


&&

.AVIATION...
(06Z TAFS)
SHRA and TSRA will increase in frequency across the area as a
tropical wave moves through. Periods of reduced VIS and low
ceilings are anticipated, especially for TJSJ and the USVI
terminals through the day, and TJBQ and TJPS after 17Z. Winds will
be from the ENE at 15 to 21 kts, gusting up to 26kts.

&&

.MARINE...
A building surface high pressure across the Atlantic will continue
to promote moderate to fresh easterly winds across the regional
waters today. Seas will remain from 3 to 5 feet with easterly
winds up to 20 knots and gusty winds near the shower activity. For
today and tomorrow a tropical wave will enhance frequent showers
across the region with thunderstorms resulting localized hazardous
marine conditions.

There is a moderate risk of rip current for all the north coastal
areas of Puerto Rico, Culebra and the U.S. Virgin Islands. The
risk will remain low for the western and southern coastal plains.

[cycloneye]

Area Forecast Discussion...UPDATED
National Weather Service San Juan PR
500 AM AST Thu Aug 22 2024

.SYNOPSIS...A tropical wave will finish moving through the area
today. A second one will move through on Sunday. A stronger wave
is expected to bring more showers and thunderstorms on Wednesday.
Temperatures will be above normal but will not fluctuate very much
from day to day.

&&

.SHORT TERM...Today through Saturday...
A variable weather pattern prevailed for the night into the early
morning hours across our area of responsibility. Isolated to
scattered showers were observed across most of the eastern
sections of Puerto Rico and the local waters, where some of those
showers briefly brushed the coastal areas of the U.S. Virgin
Islands. Although frequent shower activity was observed, rainfall
accumulations were minimal for most of the areas. In terms of
temperatures, most coastal areas experienced minimum temperatures
in the low 80s, with much cooler temperatures across the
mountains.

A variable weather pattern will persist across the region for the
rest of the morning and the afternoon due to plenty of moisture from
the passage of a tropical wave. According to derived imagery from
the GOES satellite, the moisture field remains slightly above the
climatological normal with PWAT around 1.8 to 1.9 inches.
Although a strong mid-level ridge will continue to hold during the
period, the available moisture will be enough to result in
frequent isolated to scattered showers along with thunderstorms in
the afternoon. The heaviest shower activity would result in urban
and minor flooding across western sections.

By Friday into Saturday, the bulk of the tropical moisture will move
out of the region, and a building surface high pressure across the
northern Atlantic will mostly dominate the islands. Embedded in the
easterly winds, fragments of shallow moisture will move in and out,
inducing a typical weather pattern for the islands.

Temperature-wise, the islands can expect a seasonal pattern with a
maximum near the upper 80s to the lower 90s across most of the urban
and coastal areas, with heat indices that could exacerbate health
problems in vulnerable sectors.

.LONG TERM...Sunday through Thursday...

A weak TUTT low will move slowly across the area from east to west
and will merge with the long strong upper trough on Tuesday from
Puerto Rico to the Massachusetts coast. No strong features will be
seen in the vicinity Wednesday and Thursday. At 700 mb a weak
trough is seen crossing through the area on Sunday followed by
some drier air. Better moisture moves through the area on
Wednesday ahead of and behind another tropical wave. Temperature
trends are generally muted but a warming trend is seen toward the
end of the period. Stability lessens on Sunday and remains at the
same general level through Tuesday night and then lessens again.

&&

.AVIATION...
(06Z TAFs)

VFR conditions will persist for most of the period, with
brief MVFR conditions for TJSJ & TJBQ at around 22/18Z due to afternoon
SHRA. Winds will continue from the E-SE, increasing up to 15
knots with gusty winds during the morning and afternoon. TSRA and
SHRA may result in lower ceilings across the mountains and
reduced visibility at around 22/19Z.

&&

.MARINE...Moderate to fresh winds will bring seas of 5 to 6 feet
to exposed waters today and tomorrow, with better conditions over
the weekend and into Monday. A northerly swell will continue and
turn more northeasterly Sunday and Monday. A weak tropical wave
will bring more moisture on Sunday. A better tropical wave will
bring stronger shower and thunderstorm activity Tuesday night and
Wednesday.

&&

.BEACH FORECAST...A northerly swell will bring a moderate risk of
rip currents to the north coasts of Puerto Rico, Culebra and the
U.S. Virgin Islands. Southern coasts will remain protected this
week and through much of the week ahead.
with

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
510 AM AST Fri Aug 23 2024

.SYNOPSIS...Warm and muggy days will continue with weak tropical
waves enhancing the shower activity on Sunday and Wednesday.

&&

.SHORT TERM...Today through Sunday...

A variable weather pattern prevailed from last night into the
early morning. Isolated passing showers were observed across most
of the local waters, streaming over eastern sections of Puerto
Rico and some coastal areas of the U.S. Virgin Islands. Rainfall
accumulations were minimal in most areas. Overnight temperatures
remained in the low 80s, with much cooler temperatures across the
mountains.

The islands will remain under a variable weather pattern for the
rest of the day, with easterly winds resulting from a broad surface
high-pressure system over the Central Atlantic. In terms of
available moisture, GOES satellite imagery shows PWAT values of 1.6
inches, which is sufficient to result in afternoon showers. Although
there is a high chance of showers this afternoon, widespread shower
activity is not anticipated due to the mid-level ridge persisting
for the rest of the period. Given the expected conditions, residents
can expect isolated to scattered showers along with thunderstorms in
the afternoon. The heaviest shower activity may result in urban and
minor flooding across western sections.

For the upcoming weekend, global model guidance suggests a typical
weather pattern with pockets of fragmented moisture arriving in the
area, driven by the winds. Under this pattern, with sufficient
moisture and local and diurnal effects, afternoon showers are
forecasted for each day, especially during the afternoon hours.
Minor urban flooding and small stream flooding are still possible
with the heaviest activity. On Sunday, veering winds at the surface
will result in warmer conditions and will focus the showers across
the northwestern quadrant and the San Juan Metro area.

Temperature-wise, the islands can expect a seasonal pattern with
maximum temperatures near the upper 80s to lower 90s across most
urban and coastal areas, with heat indices that could exacerbate
health problems in vulnerable sectors. Given the forecast
conditions, heat advisories and warnings will likely be issued.

.LONG TERM...Monday through Friday...

A weak TUTT low northeast of the area on Monday will merge with
the long strong upper trough on Tuesday from Puerto Rico to the
Massachusetts coast, but high pressure aloft will dominate the
local area from its center near 29 north and 49 west. No strong
upper level features will be seen in the vicinity Wednesday
through Friday. At 700 mb a weak trough is seen crossing through
the area on Sunday followed by some drier air. Better moisture
moves through the area on Wednesday ahead of and behind another
tropical wave. However, the models are weakening this features
and it is no longer expected to bring as much moisture to the area
compared to yesterday's solution. Temperature trends are
generally muted now with changes from day to day of only a few
degrees. Stability lessens on Sunday and remains at the same
general level Monday through Saturday, with the best chances of
thunderstorms on Wednesday and Thursday, although every day in
the long term period could have thunderstorms in the western and
interior portions of Puerto Rico.

&&

.AVIATION...
(06Z TAFs)

VFR conds will persist for most of the period, with brief MVFR
conds for TJBQ at arnd 23/18Z due to afternoon SHRA. Winds will
cont from the E, increasing up to 15 knots with gusty winds. TSRA
and SHRA may result in lwr CIGS across the mtns and reduced VSBY.

&&

.MARINE...

Seas today through Wednesday will gradually diminish to 3 to 4
feet in the exposed waters and to less than 2 feet in the
protected waters around the area.

&&

.BEACH FORECAST...

A northerly swell will create a moderate risk of rip currents
today through Saturday on the north coasts of Puerto Rico and
around the northeast portion of Saint Croix. As this swell begins
to come out of the northeast the areas on the north coast affected
will recede to the west. The moderate risk of rip currents will
expand again on Sunday.

&&