Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
357 AM AST Wed Jun 3 2020

.SYNOPSIS...A surface high pressure moving into the Central
Atlantic will tighten the local pressure gradient to result in
breezy conditions across the local area through the end of the
work week. Generally below-normal moisture is expected to prevail
over the area through the upcoming weekend, however, there will
still be sufficient moisture at lower-levels to generate some
afternoon convection across the western half of Puerto Rico.
Weather conditions are expected to turn more unsettled by the
early to middle portion of next week as the combination of a mid
to upper-level trough and deeper moisture will aid in enhancing
shower and thunderstorm activity.

&&

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

Below normal moisture is expected for today through Friday, which is
consistent with what the model guidance was suggesting yesterday.
However, the available moisture will be sufficient to cause some
development of locally induced showers and thunderstorms,
particularly over western Puerto Rico every afternoon. That said,
the showers and thunderstorms are not expected to be too long
lasting. Even though there is a mid to upper level trough over the
local islands, the current and forecast position for the next few
days causes northwest winds in the mid to upper levels, which is
associated with subsidence. Therefore, we are forecasting
scattered showers and isolated thunderstorms across west to
northwest Puerto Rico for today through Friday, but all mention of
numerous showers was removed. The shower and thunderstorm
activity expected today could cause ponding of water on roadways
and poor drainage areas. The prevailing wind flow in will be
mainly from the east, at around 10-15 mph, with occasional gusts
during the daytime hours from today through Thursday. The daytime
high temps will be once again in the upper 80s to low 90s across
the lower elevations, and in the low to mid 80s across the higher
elevations.

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

Generally below normal moisture will continue through the
upcoming weekend. Therefore, mostly fair weather conditions are
anticipated across most of the region. However, there will still
be sufficient low-level moisture available to combine with local
and diurnal effects to generate scattered showers and isolated
thunderstorms across the western half of Puerto Rico. Model
guidance continues to be consistent in showing a more unsettled
weather pattern by the early to middle portion of next week as a
broad mid to upper-level trough establishes over the western
Atlantic with its axis bottoming out across the northern
Caribbean. At the same time, deeper moisture is expected to pool
in with precipitable water values increasing to between 1.7 and
2.0 inches. The combination of these factors should result in a
better potential for more widespread shower and thunderstorm
activity. In addition, the steering flow is expected to be very
light, resulting in slow-moving activity. Therefore, the
potential for urban and small stream flooding will increase under
this general scenario. At this time, the best days for the most
widespread activity appears to be Tuesday and Wednesday of next
week.

&&

.AVIATION...VFR conditions expected through 03/16Z. Thereafter,
SHRA/TSRA is possible near TJBQ and TJMZ, therefore VCTS was
written on TAF. ISOL SHRA is expected elsewhere, causing brief
VCSH. Winds will be from the East at 10 to 15 knots after 03/13Z
with occasional gusts and sea breeze variations, winds becoming
light and vrb aft 03/23Z.

&&

.MARINE...Seas are expected to continue to range between 2 and 5
feet for today. However, starting later tonight and continuing
through Friday, seas of up to 6 feet are expected as the local
winds increase. There is a moderate risk of rip currents across
most of the northern and some of the southern beaches of Puerto
Rico as well as across the east-facing beaches of Culebra,
Vieques, and Saint Croix.

&&

FIRE WEATHER...Surface observations continue to indicate very dry
soils with KBDI values across Cabo Rojo and Camp Santiago at 598
and 735, respectively, as well as ten-hour fuel moisture at around
9-10%. A drier than normal air mass is expected across the area
for today, which should allow relative humidity values to drop
into the middle 40s to lower 50s. Sustained winds are expected to
peak at around 15 mph with frequent higher gusts. Therefore, an
elevated fire danger risk continues for the southern coastal
plains and a Fire Danger Statement (RFDSJU) has been issued
accordingly.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 88 79 / 20 20 20 20
STT 89 80 89 79 / 20 20 20 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
411 AM AST Thu Jun 4 2020

.SYNOPSIS...Drier than normal moisture and moderate easterly
winds will cause mainly fair weather across the local islands for
the next few days. However, some locally induced convection across
western Puerto Rico will remain possible in the afternoons.
Slightly above normal temperatures are also be expected, with
highs in the upper 80s to low 90s across the lower elevations. The
marine conditions will also be choppy for the rest of the
workweek. A change in weather pattern is expected next week,
although with considerable uncertainty, it appears that the
chances of rain will increase next week.

&&

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

Generally fair weather conditions expected to prevail across most of
the local area through the short term period as the combination of a
drier than normal air mass and a mid-level ridge will serve to limit
the shower activity. Having said this, there will still sufficient
moisture in the lower-levels to combine with local and diurnal
effects to generate scattered showers and isolated thunderstorms
across portions of western Puerto Rico each afternoon. However,
significant rainfall activity is not expected. Some brief trade wind
showers cannot be ruled out at times during the overnight and early
morning hours across portions of eastern Puerto Rico and the USVI.
Breezy conditions are also expected through the period as a broad
surface high pressure settles across the central Atlantic, helping
to tighten the local pressure gradient.

.LONG TERM...Sunday through Friday...

The weather pattern appears to change for this next week, although
there is considerable uncertainty and the model guidance has been
somewhat inconsistent with its timing and intensity, there is
consistency in the fact that some change is coming to the local
weather pattern. This change will probably mean a few days with
an increased chance of showers and thunderstorms. First of all the
local winds are expected to diminish significantly due to a
surface trough to the north of the local area, causing a COL
starting on Monday and persisting through at least Wednesday.
Although the wind direction is expected to remain mainly from the
SE, the wind speeds will diminish to 10 mph or less, in many cases
inland staying around 5 mph. There will be an increase in
moisture with precipitable water values being near to above
normal. There will also be an upper trough that will be
strengthening and will close into an upper low by the end of next
week. This upper trough will help cause instability across the
local area and provide support for thunderstorm development. That
said, the different global models differ in the timing for when we
will have the best support for thunderstorms. The GFS model being
the wetter model, especially for eastern PR, where the GFS put a
bullseye of heavy precip on Monday afternoon. Given all this
information it is worth mentioning again that uncertainty is high
in the long term forecast, especially for timing and intensity of
possible rain and thunderstorms, but it appears likely that a
change in pattern will be observed next week.

&&

.AVIATION...Mainly VFR conditions to prevail across the local area. Sct
SHRA/TSRA possible across western and northwestern PR between 04/17
and 04/22z, resulting in VCTS across TJMZ/TJBQ terminals. Winds
expected to be mainly from the E at less than 10 kts through 04/12z,
increasing to 15 to 20 kts with higher gusts and sea breeze
variations after 04/14z.


&&

.MARINE...Moderate to fresh winds from the east to east-southeast
today will result in choppy seas. The winds are expected to be up
to 20 knots with occasional higher gusts, and wave heights up to 6
feet today and on Friday. Therefore, small craft operators are
urged to exercise caution. Winds and seas are expected to improve
starting this weekend; by the following workweek, the winds are
expected to be gentle and the wave heights generally between 2-3
feet.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 80 90 78 / 10 20 20 30
STT 90 80 89 78 / 10 20 20 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
345 AM AST Fri Jun 5 2020

.SYNOPSIS...Drier than normal available moisture and moderate
easterly winds will cause mainly fair weather across the local
islands at least through Sunday. However, some locally induced
convection across western Puerto Rico will remain possible in the
afternoons. Slightly above normal temperatures continue to be
expected for the next few days, with highs in the upper 80s to low
90s across the lower elevations. The marine conditions will also
be choppy through Saturday, but will improve thereafter as winds
weaken. An increase in shower and thunderstorm activity is
expected for next week as moisture and instability increases.


&&

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

A benign weather pattern looks to continue across the local area
into the upcoming weekend. The combination of a drier than normal
air mass along with a mid-level ridge will continue to limit shower
activity. Having said this, there will still be sufficient low-level
moisture to combine with local and diurnal effects to generate
scattered showers and a few thunderstorms across western portions of
Puerto Rico this afternoon and Saturday afternoon, and across
northwestern portions of Puerto Rico Sunday afternoon as the low-
level flow becomes southeasterly. Any afternoon convection should be
short-lived, limiting rainfall accumulations. Some brief trade wind
showers are possible across portions of eastern Puerto Rico and the
USVI during the overnight and early morning hours. A surface high
pressure situated across the central Atlantic will continue to
result in brisk easterly winds today and Saturday with sustained
winds peaking between 15 and 20 mph with higher gusts. Winds are
expected to diminish significantly by Sunday and become more
southeasterly as the surface high pressure moves further east into
the Atlantic and the local pressure gradient weakens.

.LONG TERM...Monday through Saturday...

There is now more consistency among the different model runs
regarding a change in the weather pattern for this next week,
although there is some uncertainty and there is some disagreement
amongst the different models, the model guidance is consistent in
showing from run to run that the moisture and instability will
increase starting on Monday, prevailing through at least
Wednesday. An increased chance of significant showers and a few
thunderstorms over Puerto Rico and the USVI is forecast by both
the GFS and ECMWF models. The GFS has most of the rainfall on
Monday afternoon, with a bullseye once again over eastern PR,
although a larger coverage area and with more rain than it was
suggesting yesterday. The ECMWF favors Wednesday, but with more
generalized rainfall, although with lesser amounts than the GFS.
By Monday, the local winds are expected to have diminished
significantly due to a surface trough to the north of the local
area, causing a COL, which will prevail through at least
Wednesday. Although the wind direction is expected to remain
mainly from the S to SE, the wind speeds will diminish to 10 mph
or less, in many cases inland staying around 5 mph. There will be
an increase in moisture with precipitable water values being near
to above normal. There will also be an upper trough that the
models continue to insist that will be strengthening and will
close into an upper low by the end of next week. This same upper
trough will help cause instability across the local area and
provide support for thunderstorm development during the first half
of next week. For the latter part of the week, there is consensus
among the models that there will be a period of dry weather once
again. Given all this information it is worth mentioning that
there is still some uncertainty, especially when it comes to
timing and intensity of the possible rain and thunderstorms, but
it appears likely that an increase in shower and thunderstorm
activity will be observed next week.


&&

.AVIATION...Mainly VFR conditions to prevail across the local area. Sct SHRA and
Iso TS possible across western PR between 05/17z and 05/22z,
resulting in VCTS mainly across TJMZ. Winds will continue from the E
at less than 10 kts through 05/12z, increasing to 15 to 20 kts with
higher gusts and sea breeze variations after 05/14z.


&&

.MARINE...Choppy marine conditions with seas up to 6 feet and
east winds up to 20 knots are expected to prevail across the
regional waters through tonight. As a result, small craft
operators are urged to exercise caution. Marine conditions are
forecast to gradually improve during the weekend into early next
week. A moderate risk of rip currents continues for most of the
local beaches.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 89 78 / 20 30 30 10
STT 90 79 89 78 / 20 30 30 10

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
453 AM AST Sat Jun 6 2020

.SYNOPSIS...

Shallow moisture will combine with diurnal and local effects to
produce shower activity each afternoon during most of the short
term period across interior and western portions of the islands.
An increase in moisture, provided by the combination of a weak
tropical wave and an upper level through will enhance shower
activity and coverage across the islands by early next week. This
will also result in better potential for some isolated
thunderstorms across the forecast area.

&&


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

A surface high pressure located over the north central Atlantic will
maintain moderate easterly winds and breezy conditions across the
islands through today. Winds are forecast to gradually diminish late
Sunday through Monday while becoming more southeasterly. Recent GFS
model guidance suggests layered precipitable water values between
1.25-1.50 inches through today, with a gradual increase to between
1.70-1.80 inches late Sunday through Monday as a weak easterly
perturbation approaches the area. As aforementioned, the easterly
wind flow is to become more southeasterly by Sunday and Monday as
the Atlantic high lift farther northwards into the northeast
Atlantic. This will result in slightly warmer than normal
temperatures over the north coastal sections of the islands, along
with a gradual increase in tropical moisture. In general, mostly
sunny skies and fair weather conditions will prevail through the
weekend, with some passing showers during the overnight and early
morning hours over the local waters and sections of the U.S. Virgin
Islands and eastern Puerto Rico. This will be followed by afternoon
convection mainly over western sections of Puerto Rico due to a
combination of daytime heating and local terrain effects along with
limited available moisture.

On Monday similar conditions expected as far as the weather pattern,
however with the approach of an easterly perturbation expect a
slight increase in early morning and afternoon showers mainly over
the east and south coastal sections of the islands, and in the west
interior and northwest sections of Puerto Rico and west-end of the
some of the U.S. Virgin islands during the afternoon hours. Overall,
expect mostly fair weather conditions to prevail for much of the
islands during the short term period.


.LONG TERM...Tuesday through Sunday...

Model guidance is suggesting an increase in moisture and
instability by early next week and prevailing through at least
Wednesday. This will result in significant showers and a isolated
thunderstorms over Puerto Rico and the USVI. Wind direction is
expected to remain mainly from the southeast, but the wind speeds
will diminish to 5-10 mph. An increase in moisture is suggested by
the models as precipitable water is forecast to be near to above
normal values. There will also be an upper trough that the models
continue showing strengthening through the end of next week. This
feature, together with a very week tropical wave will help cause
instability across the forecast and provide support for
thunderstorm development during midweek. For the latter part of
the week, there is consensus among the models that there will be a
period of dry weather once again. However, there is still some
uncertainty in the forecast, especially when it comes to timing
and intensity of the possible rain and thunderstorms. Nonetheless,
it appears likely that an increase in shower and thunderstorm
activity will be observed next week.

&&


.AVIATION...

VFR conds at all terminals thru prd. SCT lyrs nr FL025...FL040 en
route btw local islands and ovr regional waters with Few SHRA. Sfc
Wnds calm to lgt/vrb bcmg fm E-SE 10-15 kts with ocnl hir gust and
sea breeze variations aft 06/14Z. VCSH/VCTS mainly ovr W interior of
PR 06/17Z-06/22Z with Few aftn SHRA over coastal waters.

&&


.MARINE...

Marine conditions are expected to remain choppy through tonight
due to wind driven seas with seas up to 5 feet and winds up to 20
knots. Small craft operators are urged to exercise caution across
offshore Atlantic and Caribbean waters. For the beachgoers, a
moderate rip current risk continues for most of the local beaches
for the next several days.

&&


.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 90 78 / 40 30 30 30
STT 89 78 88 78 / 20 20 20 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
446 AM AST Sun Jun 7 2020

.SYNOPSIS...

Moisture associated with a weak surface trough will promote
shower activity today. A tropical wave will approach the islands
by early this week and will bring a surge in moisture. This will
result in an increase is shower activity and coverage with
isolated thunderstorms mainly in the afternoons. This active
weather pattern will hold through the end of the week. Thus, a
more calmer weather is expected by next weekend into the workweek.
Winds and seas slightly subside, with seas generally below 5 feet
and winds up to 15 knots across the regional waters.

&&

.SHORT TERM...Today through Tuesday...

A surge of moisture associated with a weakly induced surface trough
will cross the region today, steered by a moderate east to southeast
low level wind flow. By Monday and through Tuesday, a tropical wave
is expected to move across the northeastern Caribbean bringing
additional moisture to the region. This along with the proximity of
a meandering mid to upper level trough (TUTT) will maintain fairly
unstable condtions across the region resulting in enhanced overnight
and early morning showers with possibly isolated thunderstorms each
day.

For the rest of today, expect the early morning passing showers to
continue to affect the regional waters and portions of the east and
south coastal areas of the islands. This will promote brief periods
of moderate to locally heavy rains. Afternoon shower development
should be focused mainly over parts of the west-end of the U.S.
Virgin Islands, as well as over the central and west interior
section of Puerto Rico. Some afternoon showers will also be possible
in and around the San Juan metro but in the form of streamer like
convection which will move in and out or the area. That said, urban
and small stream flooding will be possible particularly over
portions of central interior and and western Puerto Rico.

As previously mentioned for Monday and Tuesday expect a gradual
increase in the instability aloft along with increasing moisture
transport as the tropical wave approaches. This in turn will favor
better potential for showers and isolated thunderstorm development
in and around the islands with increasing chance for urban and small
stream flooding, as well as ponding of water on roadways and in poor
drainage areas. During the period, so far the best potential for
enhanced daytime convection will be on Tuesday based on latest
guidance.


.LONG TERM...Wednesday through Monday...

A cold front associated with the low pressure will continue to
promote an increase in moisture across the region through at least
Thursday. Precipitable water values will increase to around 1.9
inches for the middle of the week. Together with an upper level
trough just west of the forecast area will provide enough
instability to produce shower and thunderstorm activity over land
areas and surrounding waters. These showers are expected to focus
mainly over interior and northwestern sections and will produce
moderate to locally heavy rains in the afternoons. Although this
weather pattern is not as conducive for widespread heavy rain
over Puerto Rico, urban and small stream flooding are possible
with the heaviest and most persistent rains.

A more seasonal weather pattern is expected across the forecast
area by the end of the week into the workweek. A high pressure is
once again expected to dominate the central Atlantic, which will
help the low-level easterly winds to pick back up. The usual
patches of moisture embedded in the easterly winds will enhance
shower activity. With ridging at mid to upper levels, these
showers are not expected to be significant, as substance and
dryness from ridging will inhibit the vertical development of
these showers.

&&


.AVIATION...

VFR conds at all terminals. SHRA/Isold TSRA ovr regional waters and
en route btw islands. SCT ocnl BKN lyrs nr FL025...FL050...FL120.
SHRA/ Isold TSRA and SCT-BKN at FL022-040 may result in brief MVFR
at TJMZ/TJBQ btw 07/16-23Z. VCSH at TSJU/TNCM/TKPK fm 07/07Z-07/14Z
and aft 07/17Z. Winds light and variable bcmg fm E-SE 12-15 mph with
hir gusts aft 07/14Z.

&&


.MARINE...

A surface high pressure across Central atlantic will promote a
gentle to moderate east wind flow across the regional waters for
much of the period. Tranquil marine condtions are expected across
the local waters with seas up to 5 feet. Shower and isolated
thunderstorm activity will increase towards the middle of next
week. For the beachgoers, there is a moderate risk of rip currents
for along the northern coast of Puerto Rico, including the
eastern coast of Vieques, Culebra and St. Croix.

&&


.PRELIMINARY POINT TEMPS/POPS...
SJU 90 77 89 76 / 30 20 40 40
STT 88 81 87 81 / 20 10 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
450 AM AST Mon Jun 8 2020

.SYNOPSIS...
Overnight and morning showers will continue to affect the local
waters and portions of the east and south coastal areas of the
islands from time to time. Afternoon showers and thunderstorm
development will be likely mainly across the interior and western
Puerto Rico, as well as downwind from the rest of the islands,
including El Yunque in eastern Puerto Rico and around the San
Juan Metro area. An increase in moisture and instability aloft
is expected at least until Wednesday, with the passage of a weak
tropical wave along with favorable conditions in the mid to upper
levels. This will enhance afternoon convection across portions of
the islands. Thus, there is good potential for urban and small
stream flooding as well as mudslides in areas of steep terrain
especially over the west interior sections of Puerto Rico.

&&

.SHORT TERM...Today through Wednesday...
As the weak tropical wave approaches, expect a gradual increase
increase in moisture content across the forecast area. This,
together with a trough of low pressure aloft will increase the
instability and favor better potential for afternoon showers and
isolated thunderstorm development over the interior and west
sections of the islands, as well as the surrounding waters and
around the U.S.Virgin Islands. As result, an increasing chance
for urban and small stream flooding, as well as ponding of water
on roadways and in poor drainage areas is expected. Based on the
latest model guidance, the best potential for enhanced daytime
convection will be on Tuesday. Winds will generally be from the
east at the surface, becoming very light just above the surface.
These light winds will help showers easily develop and linger over
western and interior sections of Puerto Rico. However, streamer
like showers down from El Yunque and the USVI cannot be ruled out
each afternoon.

.LONG TERM...Thursday through Tuesday

Occasional patches of trade wind moisture along with that from
an old frontal boundary and weak surface surface trough will
continue to move across the region through at least the end of
the work-week. This along with an upper level trough just north
and west of the region will provide sufficient instability to
support shower and thunderstorm development over land areas and
the coastal waters each day. These showers should be focused
mainly over the interior and northwestern sections of Puerto Rico,
and will produce periods of moderate to locally heavy rains during
the afternoons,with possible isolated enhanced thunderstorm
activity. Although widespread heavy rainfall is not anticipated
over Puerto Rico, urban and small stream flooding will remain
possible in isolated areas with the heaviest and most persistent
rains. During this time, a few showers may also affect the U.S.
Virgin islands especially during the early morning hours, with
only isolated activity expected during the afternoon. These
showers will be of short duration with no significant rainfall
accumulations forecast at this time.

For the following weekend, A more seasonal weather pattern is expected
across the area, as a surface high pressure is once again expected
to dominate the central Atlantic,and a ridge of high pressure will
build aloft and spread across the region from the west. This pattern
will favor increasing trade winds over the weekend into early next
week with winds becoming more east southeast. That said, expect the
typical patches of tradewind moisture embedded in the easterlies,
which will help to enhance afternoon shower development each day.
With ridging to hold in the mid to upper levels, the daytime
shower activity is not expected to be significant or widespread as
subsidence and drying aloft will inhibit the vertical development.
However good daytime heating due to the southeasterly wind flow
may still favor isolated thunderstorms over the interior sections
of Puerto Rico.

&&

.AVIATION...Mainly VFR conditions are expected through much of the
forecast period. VCTS might cause TEMPO groups at TJMZ/TJBQ after
03/18Z. Thus, with MVFR conditions are anticipated due to low
ceilings and reduced VIS. Winds will be generally light and variable
through 08/12Z. Then, winds will be shifting from the east at 10 to
15 knots for the rest of the period.


&&

.MARINE...Tranquil marine conditions with seas below 5 feet and winds
up to 15 knots are expected across the regional waters through most
of the workweek. There is a low risk of rip currents for all local
beaches through at least Wednesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 77 88 78 / 20 40 60 40
STT 89 77 87 76 / 30 50 50 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
532 AM AST Tue Jun 9 2020

.SYNOPSIS...
A meandering and gradually amplifying mid to upper level trough
and a weak tropical wave crossing the eastern Caribbean, will increase
instability aloft and low level moisture transport across the forecast
area today through Wednesday. A broad surface high pressure ridge over
the north central Atlantic, will help to maintain a fairly light east
to southeast wind flow across the region through the end of the workweek.
This pattern will increase the potential for showers and thunderstorm
development in and around the islands and coastal waters through
Wednesday. A gradual improvement is expected by the end of the
workweek as a drier airmass is forecast to move across the region
and an upper level ridge builds aloft.

&&

.SHORT TERM...Today Through Thursday...

The combination of the weak tropical wave and a mid to upper
level trough over the Atlantic calls for moist and unstable weather
conditions through most of the short term period. These features
will increase low level moisture convergence across the area. That
combined with local effects and daytime heating, will increase the
potential for widespread showers and isolated thunderstorm activity
across the area during the afternoons. Due to slow steering flow
and warm temperatures, these showers will be persistent mainly over
portions of western and interior sectors of the islands, but will
drift towards the west and south coastal areas later in the afternoon.
The main threat for these areas will be urban and small stream flooding
with the heaviest and most persistent rains. Some streamer- like shower
activity downwind from El Yunque cannot be ruled out and therefore
the San Juan metro area could also observe active weather during
the afternoon hours. There is good potential for isolated thunderstorm
activity during the afternoon mainly due to daytime heating, local
forcing and the proximity of the amplifying upper- level trough.
Moisture embedded in the easterly windflow will continue to bring
passing showers in and around the islands during the overnight
hours.

.LONG TERM...Friday through Wednesday...
Upper level trough is to weaken and lift northwards by Friday
into the weekend, as a mid to upper level ridge will build aloft.
This will support a somewhat drier airmass and a prevailing southeast
low level wind flow as the broad surface high pressure will hold
across the north central Atlantic. A weak easterly perturbation is
forecast to move just south of the region late Friday through early
Saturday and this will provide sufficient moisture across the region
to maintain periods of passing overnight and early morning
showers. This will be followed by isolated to scattered afternoon
convection mainly over parts of the central interior and northwest
sections of Puerto Rico. A few showers will also be possible mainly
downwind or just off the northwest coastal areas of the rest of
the islands including the U.S. Virgin Islands but mostly sunny skies
should prevail.

For the remainder of the weekend and into the following week, a
more seasonal weather pattern is expected, as a surface high pressure
is forecast to dominate the central Atlantic, along with a ridge
of high pressure which will build aloft and spread across the region.
This pattern should favor increasing trade winds over the weekend
into early next week with winds becoming southeasterly. Expect the
typical patches of tradewind moisture embedded in the easterlies,
which will help to enhance afternoon shower development each day.
The daytime shower activity is not expected to be significant or
widespread, as subsidence and drying aloft will inhibit the vertical
development. Good daytime heating however along with local forcing
due to the moderate southeasterly wind flow may still favor isolated
afternoon thunderstorms over the west and interior sections of Puerto
Rico.

&&

.AVIATION...Mainly VFR conditions are expected through much of the
forecast period. However, TSRA/SHRA might result in MVFR conditions
at TJMZ/TJBQ after 09/15Z. Thus, SCT-BKN ceilings and reduced VIS
are anticipated across those terminals. Iso to Sct SHRA possible
around the USVI after 09/22z, resulting in VCSH across TIST and
TISX. Low-level winds will be generally light and variable through
09/12Z. Then, winds will be shifting from the east at 10 to 15 knots
for the rest of the period.

&&

.MARINE...A light to moderate east to southeast wind flow will prevail
across the regional waters through the workweek, as a broad surface
high pressure will dominate the north central Atlantic. This will
result in fairly tranquil seas of less than 5 feet. A weak tropical
wave will continue to cross the region waters today through Wednesday
to increase the chance for showers and isolated thunderstorms
across portions of the local waters.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 78 89 78 / 40 40 40 40
STT 89 78 88 78 / 30 30 50 50

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
408 AM AST Wed Jun 10 2020

.SYNOPSIS...The combination of a mid to upper-level trough extending
across the region, an induced surface trough and a tropical wave now
crossing the Caribbean waters, will maintain a very moist and unstable
airmass. This will favor unsettled weather conditions across the
forecast area at least through Thursday. These features along with
the fairly light steering flow will support periods of persistent
afternoon shower and isolated thunderstorms activity. Therefore,
urban and small stream flooding will be likely during the afternoons
at least until the end of the workweek. A gradual improvement is
expected by Friday and into the weekend, as a high pressure ridge
is to build overhead and the surface high pressure spreads across
the central and northeast Atlantic. By then, low level winds will
become southeasterly and as a result, daytime high temperatures
will range from the upper 80s to the low 90s along the north
coastal sections including the San Juan metro and surrounding
areas.

&&

.SHORT TERM...Today Through Friday...

The tropical wave moving through the Caribbean waters and the mid
to upper-level trough north of the forecast area will continue to
cause unstable weather conditions through Friday. Therefore,
showers and thunderstorms are expected over the interior and the
western portions of Puerto Rico. The combination of relatively
saturated soils, light steering winds, and additional rainfall as
a result of modest instability provided by the mid to upper-level
trough and local and diurnal effects will likely cause urban and
small stream flooding during the afternoons for several areas.

By Friday, the upper level trough is expected to weaken and move up
north. Meanwhile, a mid to upper level ridge will start building
aloft. This combination will support the entrance of a somewhat
drier air mass over the forecast region as well as a prevailing
southeast wind flow at the low levels. However, the proximity of a
weak tropical wave will bring enough moisture to enhance shower
activity across interior and northwestern portions of the islands in
the afternoon hours. Rainfall accumulations are anticipated to be
minimal with this activity. Overall, mainly fair weather conditions
with sunny to partly cloudy skies should prevail by the end of the
short term period.

.LONG TERM...Saturday through Thursday...

Upper level trough is to weaken and lift northwards through the
weekend, as a mid to upper level ridge will build overhead. This
will support a much drier airmass and a prevailing southeast low
level wind flow as the broad surface high pressure will spread
and hold across the central and northeast Atlantic. Weak low level
easterly perturbations are forecast to move just south of the region
through Saturday and this will provide sufficient moisture across
the region to maintain periods of passing overnight and early morning
showers. This will be followed by locally and diurnally induced
afternoon convection mainly over parts of the central interior
and northwest sections of Puerto Rico. A few showers will be possible
around the U.S Virgin Islands, but should be mainly downwind or just
off the northwest coastal areas. Mostly sunny skies should prevail
elsewhere.

For the remainder of the weekend and into the following week, a more
seasonal weather pattern is expected, as the surface high pressure
is forecast to dominate the central Atlantic, along with a strong
ridge of high pressure aloft. This pattern should favor increasing
trade winds during the early part of next week. Expect patches of
tradewind moisture embedded in the easterlies to continue to affect
the region. This will aid in afternoon shower development each day
over the interior and west sections of Puerto Rico, and mainly downwind
of the U.S. Virgin Islands. Daytime convection is not expected to be
widespread, as subsidence and drying aloft will inhibit the vertical
development at least through Tuesday. However, good daytime heating
along with local forcing and a moderate southeasterly wind flow should
favor isolated afternoon thunderstorms over the west and interior
sections of Puerto Rico each day. The next tropical wave is so far
forecast to approach the region by Wednesday. This will again increase
potential for showers and thunderstorm development across the forecast
area.

&&

.AVIATION...Mainly VFR conditions are expected through much of the
forecast period. However, VCTS is forecast for TJPS, TJMZ, and TJSJ
after 10/16Z. MVFR conditions are possible due to SCT-BKN ceilings
and reduced VIS across those terminals. Iso to Sct SHRA possible
elsewhere after 10/16z, resulting in VCSH across TIST and TISX.
Low-level winds will be generally light and variable through
09/12Z. Then, winds will be shifting from the east southeast at 10
to 15 knots for the rest of the period.

&&

.MARINE...Tranquil marine conditions expected for the next
several days with seas up to 4 feet and winds generally at 10
knots or less. There is a low risk of rip currents across all of
the local beaches.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 90 78 / 40 40 50 30
STT 88 78 88 78 / 50 40 50 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
453 AM AST Thu Jun 11 2020

.SYNOPSIS...Unsettled weather conditions with enhanced shower and
thunderstorms development are expected today, particularly during
the afternoon hours. As a result, the threat for flooding, as
well as for mudslides near areas of steep terrain is high. This
pattern is supported by abundant moisture from the a tropical
wave streaming across the Caribbean and favorable conditions aloft
from an upper level low located over the northwestern Caribbean.
A similar weather pattern is expected on Friday, but a gradual
improvement is expected during the weekend into early next week
with the entrance of drier air and a developing ridge of high
pressure aloft.


&&

.SHORT TERM...Today Through Saturday...

Another active weather day is expected across the local area. The
combination of abundant moisture from a weak tropical wave located
near La Hispanola and an upper-level low near eastern Cuba is
expected to result in enhanced shower and thunderstorm activity this
afternoon along and northern of the Cordillera Central, including
the San Juan metro area as the low-level flow changes to the east-
southeast. Given that the soils across portions of interior Puerto
Rico are saturated from the heavy rainfall activity experienced
during the last couple of afternoons, the potential will exist for
urban and small stream flooding as well as mudslides in areas of
steep terrain. Across the USVI, isolated to scattered shower
activity is possible from time to time, however, significant
rainfall accumulations are not expected.

Weather conditions will continue to remain unsettled on Friday as
the moisture content is expected to remain pretty high with
precipitable water values expected to range between 1.8 and 2.0
inches. Therefore, another round of heavy showers and thunderstorms
is expected along and north of the Cordillera Central. Once again,
urban and small stream flooding will remain a threat. Across the
USVI, some showers are possible, however, once again significant
rainfall accumulations are not expected.

On Saturday, a tropical wave currently located east of the Windward
Islands is expected to move across the Caribbean waters. Model
guidance keeps the heaviest activity associated with the wave to the
south of the islands, however, the associated moisture is expected
to move over the area. As this moisture combines with local and
diurnal effects, another round of afternoon convection is likely,
mainly across northwestern Puerto Rico.


.LONG TERM...Sunday through Friday...

A surface high pressure across the central Atlantic will maintain
a generally light to moderate east to east-southeast surface wind
flow across the region. A typical seasonal pattern with patches of
low-level moisture streaming across the region is expected. This
pattern is defined by overnight and early morning showers moving
from the waters into coastal areas of eastern Puerto Rico and the
USVI, followed by afternoon convection along the interior and
western sectors of Puerto Rico. Streamer- like showers are also
possible downwind from El Yunque and the local islands into
eastern Puerto Rico and the San Juan metropolitan area each
afternoon. Although conditions aloft with a strong trade wind cap
and drier air are not expected to support deep convective
development, diurnal heating along with local forcing may provide
the necessary support for isolated thunderstorm development each
afternoon. Model guidance suggests that the passage of a tropical
wave may enhance the potential for shower and thunderstorm
development by midweek.


&&

.AVIATION...Mainly VFR conditions expected to prevail through 11/16z.
SHRA/TSRA expected across interior, western, and northern PR between
11/16z through 11/22z, affecting the vicinity of TJSJ/TJBQ/TJMZ.
Tempo MVFR to possibly IFR conditions are possible. Iso to sct SHRA
possible elsewhere, however, no significant impacts to operations
expected. Winds will continue light and variable through 11/12z,
increasing to 10 to 15 kts from the E-ESE with sea breeze variations
after 11/14z.


&&

.MARINE...Fairly tranquil marine conditions with seas below 5 feet
and easterly winds up to 10 knots are expected today. Although
winds are expected to increase and become more southeasterly by
Friday into the weekend, fairly tranquil marine conditions will
hold across the local waters. Isolated to scattered showers are
forecast to stream across the local waters from time-to-time.
There is a low risk of rip currents for all local beaches.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 91 78 / 40 30 60 30
STT 88 79 87 79 / 40 40 30 30

[cycloneye]

 https://twitter.com/TTWeatherCenter/status/1271098120349405185

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
422 AM AST Fri Jun 12 2020

.SYNOPSIS...Unsettled weather conditions with enhanced shower and
thunderstorms development, as well as the potential for flooding,
rapid rises along rivers, and mudslides near areas of steep
terrain, are expected today. Although a gradual improvement is
expected during the weekend into early next week, locally and
diurnally induced showers are forecast to develop each afternoon.
Periods of enhanced shower and thunderstorm activity are expected
once again by midweek and the end of the workweek into the
upcoming weekend with the passage of tropical waves across the
eastern Caribbean.


&&

.SHORT TERM...Today Through Sunday...

An active weather pattern is expected to linger today. A mid to
upper level low remains to the northeast of the region, while a mid
to upper level ridge builds just to the east of the Lesser Antilles.
At the lower levels, a tropical wave will be entering the eastern
Caribbean later today. Additionally, moisture content remains high
around the islands, with precipitable waters ranging around 1.6 to
1.8 inches. Due to a combination of instability provided by the low,
elevated moisture levels and local effects, showers and
thunderstorms are expected to develop once again across Puerto Rico.
Winds are expected more from the southeast today, remaining light,
due to a surface trough and high pressure over the Atlantic, hence
the main focus of rain will be around the interior and northwestern
Puerto Rico. Additional activity might develop downwind from El
Yunque affecting the San Juan metro area. Since soils are saturated
due to previous rainfall, urban and small stream flooding shall
continue to occur in areas where the heaviest rainfall are
registered.

For Saturday, as the tropical waves crosses the Eastern Caribbean,
the bulk of the activity should remain south of the islands.
However, moisture will reach the area, resulting in passing showers
over eastern Puerto Rico and the U.S. Virgin Islands through the
day, followed by another round of convection around the interior and
north-northwest Puerto Rico. A similar pattern is anticipated for
Sunday, with another easterly perturbation reaching the forecast
area. However, instability aloft is expected to decrease as a mid to
upper level ridge develops over the area. This should act to delay
afternoon activity, but showers and isolated thunderstorms are still
expected to develop over western Puerto Rico.

.LONG TERM...Monday through Saturday...

A surface high pressure across the central Atlantic will maintain
a generally moderate to locally strong east surface wind flow
across the region. Variations in the flow can be expected with
the passage of two independent tropical waves by Tuesday and
Friday. In terms of shower activity, a typical seasonal pattern
is expected to dominate the local weather conditions. That is,
overnight and early morning showers moving from the waters into
coastal areas of eastern Puerto Rico and the USVI, followed by
locally and diurnally induced shower and thunderstorm development
along the interior and western sectors of Puerto Rico, as well as
downwind from El Yunque and the local islands into eastern Puerto
Rico and the San Juan metropolitan area each afternoon. However,
an increase in shower and thunderstorm development is expected as
the aforementioned tropical waves stream across the region.
Although of convective nature, the first pulse is expected
between Tuesday and Wednesday with model estimated precipitable
water peaking near 2.0 inches by Tuesday evening. Even higher
model- estimated precipitable water vapor up to 2.2 inches are
expected with the second wave, which is forecast to arrive by
Friday and affect the area through the weekend. As a result,
enhanced shower and thunderstorm activity will increase the
potential for flooding, rapid rises along rivers and mudslides
near areas of steep terrain across the local islands. Overnight
low temperatures are expected to drop into the mid to upper 70s,
while daytime high temperatures are forecast to peak into the mid
80s to low 90s across coastal areas. Since uncertainties increase
with time and both waves are expected to arrive on day 5 and 8 of
the medium to long-range period, there is medium confidence in
this forecast.


&&

.AVIATION...Mainly VFR conditions are expected to prevail through
the period. VCTS are expected after 16Z for TJMZ/TJBQ, with possible
TEMPO groups for low ceilings and reduced VIS to MVFR or IFR.
VCSH are expected elsewhere. Winds will be out of the southeast at
5 to 10 knots.


&&

.MARINE...Fairly tranquil marine conditions are expected to
continue, with seas below 5 feet and east to southeast winds up
to 15 knots are expected today. These conditions will prevail
through at least midweek. Isolated to scattered showers and a few
isolated thunderstorms are forecast to affect the local waters
from time-to-time. There is a low risk of rip currents for all
local beaches.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 91 79 / 50 20 40 20
STT 89 80 88 80 / 40 30 20 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
520 AM AST Sat Jun 13 2020

.SYNOPSIS...A generally light to moderate east to southeast
surface wind flow will prevail through late tonight, increasing
on Sunday into early next week. Although a gradual improvement in
the weather conditions is expected, rounds of locally induced
showers and thunderstorms are expected each afternoon. As a
result, the potential for urban and small stream flooding, rapid
rises along rivers, and mudslides near areas of steep terrain will
continue. A series of tropical waves will enhance shower and
thunderstorm activity by midweek and the end of the workweek into
the upcoming weekend, respectively. Tranquil marine conditions
will prevail across the region during the next few days.


&&

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

Partly to variably cloudy skies prevailed across Puerto Rico and the
US Virgin Islands during the overnight hours. Passing showers were
observed across coastal sections of eastern Puerto Rico and Saint
Thomas. Rainfall totals associated with these showers, however, were
minimal. Overnight temperatures were in the upper 70s to lower 80s
across the coastal locations. Winds were light and variable.

A mid to upper level ridge will continue to build across the
local islands with heights raising through the forecast cycle.
At lower levels, a tropical wave will continue to move mainly south
of the area with bulk of moisture remaining over the Caribbean
waters. The prevailing light to moderate east to southeast wind flow
is expected to increase somewhat through the weekend. Moisture
continues to pool across the forecast area with precipitable water
vales near or above the normal range which is 1.75 inches.

Although a ridge pattern is expected to build across the forecast
area; available moisture, diurnal heating and the sea breeze
convergence will continue to result in showers and thunderstorms
across north central, northwest and west Puerto Rico this afternoon.
Soils are already saturated, particularly across the western
interior of the island, therefore the threat of urban and small
stream flooding continues. Afternoon showers with thunderstorms are
still expected Sunday and Monday, however, the intensity and
coverage are expected to decrease as the ridge pattern establishes
across the northeast Caribbean. Elsewhere, the chances of rain are
much lower, therefore only isolated to scattered showers with minor
accumulations are in the forecast for the USVI and eastern PR.

.LONG TERM...Tuesday through Sunday...

A surface high pressure across the central Atlantic will maintain
a generally moderate to locally fresh east surface wind flow
across the region. However, winds are forecast to increase and
favor a more east-southeast flow with the passage of two
independent tropical waves. The first wave is expected to affect
the area between Tuesday and Wednesday. Although this wave is
expected to stream across the eastern Caribbean and south of the
local islands, an increase in moisture is expected, resulting in
enhanced locally and diurnally induced shower and isolated
thunderstorm development, particularly in the afternoon. Improved
weather conditions with a typical seasonal shower pattern is
expected on Thursday and Friday. Then, model guidance suggests
that a strong tropical wave will move into the eastern Caribbean
on Friday and affect the region through late Friday night into
Saturday. Since the bulk of the wave is forecast to cross the
forecast area, it will not only enhance locally and diurnally
induced convection, but it will also enhance showers and
thunderstorms moving inland from the waters. With the passage of
each wave, the potential for flooding, rapid rises along rivers
and mudslides near areas of steep terrain will increase,
particularly with the second wave since favorable conditions aloft
may support deep convective development and higher rainfall
accumulations. An improvement in the weather conditions is
expected once again on Sunday into early next week with the
entrance of relatively drier air.

Overnight low temperatures are expected to drop into the mid to
upper 70s, while daytime high temperatures will peak into the mid
80s to low 90s across coastal areas. Considering that
uncertainties increase with time, there is medium confidence in
this forecast since these waves are expected to arrive on day 4
and 8 within the medium- to long-term range period.


&&

.AVIATION...With the passage of each wave, the potential for
flooding, rapid rises along rivers and mudslides near areas of
steep terrain will increase, particularly with the second wave
since favorable conditions aloft may support deep convective
development and higher rainfall accumulations.


&&

.MARINE...Tranquil marine conditions continue with seas expected to
generally remain less than 4 feet through late tonight. A slight
increase in winds and seas is expected early next week, but
marine conditions are expected to remain tranquil. A low risk of
rip currents is expected across all of the local beaches today,
but a moderate risk is forecast for beaches along the north coast
of Puerto Rico and Culebra this evening. The moderate risk will
spread to beaches across the southern coast of Puerto Rico,
Vieques, and the USVI during the next few days.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 78 91 78 / 20 20 20 20
STT 89 80 87 78 / 30 20 20 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
501 AM AST Sun Jun 14 2020

.SYNOPSIS...Although generally stable weather conditions will
prevail through Tuesday, enough moisture along with local effects
and diurnal heating will support shower and isolated thunderstorm
development across the interior and western sections of Puerto
Rico is expected each afternoon. The passage of a tropical wave
across the eastern Caribbean and south of the local islands is
expected to enhance shower and thunderstorm activity by midweek.
Enhanced activity is also expected by the end of the workweek with
the passage of another tropical wave closer to the area. A
generally moderate to locally fresh east to southeast wind flow
will prevail through the workweek, resulting in warmer temperature
and locally choppy marine conditions.


&&

.SHORT TERM...Today through Tuesday...

A mid to upper level ridge will prevail over the local area, which
will cause more stable conditions. However, there is still enough
moisture to combine with the diurnal heating and the local effects
to cause showers and isolated thunderstorms in areas of convergence
such as the interior into northwestern Puerto Rico as well as
portions of the San Juan Metro as showers stream off the Luquillo
Mountain Range. This pattern is expected every afternoon through
Tuesday, while isolated to scattered brief showers are expected
during the overnight and early morning hours. However, since the
islands will experience a reduction in instability at the mid and
upper levels, the afternoon activity is not expected to be as
intense, as long lasting, or as widespread as it was late last week.
That said, urban and small stream flooding will remain possible due
to saturated soils causing quick runoff. The local winds are
expected to increase to 15-20 mph starting on Monday.

.LONG TERM...Wednesday through Monday...

A surface high pressure across the central Atlantic will maintain
a generally moderate to locally fresh east surface wind flow
across the region. Overall, a typical seasonal weather pattern is
expected with the most intense shower activity favoring the
interior and western sections of Puerto Rico, as well as downwind
from the local islands and El Yunque into eastern Puerto Rico and
the San Juan Metropolitan area each afternoon. Elsewhere, isolated
to scattered showers with light rainfall accumulations cannot be
ruled out. Model guidance continues to suggest that the passage of
tropical waves will enhance shower and thunderstorm activity. This
activity will favor convective development supported by local
effects and diurnal heating, as well as advective with showers
moving from the waters into coastal areas of eastern Puerto Rico
and the USVI. Lingering moisture from the first wave is expected
to persist over the area through Wednesday, while the second wave
is now expected to influence the local weather conditions by late
Thursday night through late Friday night, instead of Saturday as
suggested by previous model guidance. Thereafter, the entrance of
drier air will support relatively fair and stable weather
conditions, but locally induced showers and isolated thunderstorms
cannot be ruled out each afternoon. Considering that
uncertainties increase with time and considerable changes in
recent model guidance, there is medium confidence in this
forecast.


&&

.AVIATION...VFR conds will prevail today at most of the TAF
sites. Between 14/19- 22Z, brief periods of MVFR conds are
possible in and around TJMZ/TJBQ due to SHRA/TSRA. TJSJ will is
forecast to observe VCSH/VCTS during that time. Winds will remain
from the E-ESE at 10- 15 knots with sea breeze variations. Winds
will become light and variable after 14/23Z.


&&

.MARINE...Small craft operators are urged to exercise caution due
to locally fresh winds up to 20 knots across the coastal waters of
northern Puerto Rico. Elsewhere, winds will remain at or below 15
knots. Despite of this, tranquil seas at 5 feet or below are
expected across the local waters through the workweek. There is a
moderate risk of rip currents for beaches along the north east of
Puerto Rico and Culebra, as well as the Botany beach in Saint
Thomas. The moderate risk is forecast to spread for beaches along
the south coast of Puerto Rico, Culebra and Vieques, as well as
the eastern coast of Saint Croix this evening.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 79 90 79 / 40 20 20 20
STT 90 81 89 78 / 20 30 20 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
525 AM AST Tue Jun 16 2020

.SYNOPSIS...

A seasonal pattern is expected again today, with quick passing
showers this morning and again tonight over the local waters and
pushing onshore in portions of southeastern Puerto Rico and the
USVI. Afternoon showers with isolated thunderstorms are expected
during the afternoon, especially in northwestern and interior
Puerto Rico. Streamers are also expected to develop, some of which
will likely impact the San Juan metro area. Though gradual drying
is anticipated as we make our way into the latter half of the
week, afternoon showers are still expected each day, especially in
northwestern Puerto Rico.

&&

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

A mid-level ridge north of the region will prevail through the short
term period. This will keep moisture trapped below 700 mb and breezy
east to southeast trades for the next few days. For today, a surge
in low-level moisture is moving from the east with the trade winds.
This will result in quick passing showers across the U.S. Virgin
Islands and across the eastern third of Puerto Rico through the
morning hours. This moisture will enhance the diurnally induced
afternoon convection across the islands, and moderate to locally
heavy rainfall is expected mainly over the interior and western
sections of PR. Streamers are expected to develop off the USVI and
from el Yunque into the San Juan metropolitan area. Fair weather
conditions return on Wednesday with diurnal activity expected mainly
over west/northwest PR. Between late Wednesday night and Thursday, a
small surge in moisture is expected across the region as a tropical
wave is forecast to pass mainly south of the region. A quick drying
trend is expected by late Thursday afternoon, as a drier air mass
and a Saharan Air Layer filter from the east.

.LONG TERM...Friday through Wednesday...

As we make our way into the end of the week, increasing moisture is
expected to move over the region, with a tropical wave passing by
the area to the south on Saturday. However, even with the increase,
moisture levels are expected to remain near-normal. Meanwhile, a mid-
to upper-level ridge persists over the area, maintaining stability
aloft, which will act to inhibit, but not prevent, shower activity
and convective development. Local effects and diurnal heating will
cause showers with isolated thunderstorms in northwestern and
interior Puerto Rico, with more scattered shower activity elsewhere.
Passing showers are also likely during the overnight and morning
hours.

Sunday brings the start of a drying trend, which will continue into
Monday. The ridging aloft will also persist, though it is forecast
to weaken a little through the end of the weekend. Decreasing shower
activity is anticipated, though there will likely still be some
showers in northwestern and interior Puerto Rico, with the potential
for isolated thunderstorms.

During the day on Tuesday, the trend is expected to reverse.
Tropical moisture pulled northward by an old frontal boundary is
expected to drop down to the south over the area. Furthermore, an
upper-level trough is forecast to encroach on the ridge from the
west, likely to around Hispaniola by late in the day. As such, the
expectation is for divergence aloft to make for conditions to become
more favorable for the development of showers and thunderstorms.
During the afternoon, showers and isolated thunderstorms are likely
in western and interior Puerto Rico, and possibly in southwestern
Puerto Rico, with the flow shifting to become more northeasterly;
isolated to scattered showers will be seen in other portions of the
local islands. Though moisture is expected to diminish somewhat for
Wednesday, it will still be sufficient to aid in the development of
afternoon convection, with precipitable water amounts remaining
within seasonal normals. Additionally, the upper-level trough will
linger over the area or just to our west, providing more unstable
conditions aloft. With more easterly winds forecast for the day, the
peak in activity is currently expected to be in western and interior
Puerto Rico.

&&

.AVIATION...

Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. However, trade wind showers will
move at times across the USVI/Eastern PR terminals through the
morning hours. Then, SHRA/TSRA is expected to develop over western
PR btw 16z-22z which may cause tempo MVFR conds at TJMZ/TJBQ. Low
level wind ESE at 10-20 kt with higher gusts and sea breeze
variations after 14z.

&&

.MARINE...

Choppy seas continue over much of the local waters, associated
with moderate to locally fresh winds across the area. However,
seas are expected to remain generally less than 5 feet over the
next several days. With winds up to 20 knots anticipated over
portions of the local waters, especially in the nearshore Atlantic
waters of Puerto Rico, operators of small craft are urged to
exercise caution. With the arrival of a tropical wave this
weekend, increasing winds and building seas are forecast.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 79 90 78 / 40 50 40 20
STT 90 79 89 79 / 40 50 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
447 AM AST Wed Jun 17 2020

.SYNOPSIS...

Decreasing shower activity is expected over the next few days,
though afternoons will still see showers over western and
interior Puerto Rico. Streamers are also expected to form off of
the USVI and other islands. Breezy conditions will persist across
the area, as well, and will contribute to continuing choppy
conditions over the local waters. Starting tomorrow, hazy skies
are expected, as a substantial Saharan Air Layer filters in over
the area.

&&

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

A mid-level ridge will continue just to our north for the next
several days. This will promote stable conditions aloft and warmer
500 mb temps than previous days. A broad surface high pressure will
build gradually across the central Atlantic and moderate to fresh
trades will bring the occasional quick passing showers and small
surges of low-level moisture across the region. This will be enough
to trigger shallow afternoon convection over western PR and from
streamers developing off the U.S. Virgin Islands and smaller
islands. Drier air and a Saharan Air Layer filters later on Thursday
and peaks during the weekend. Therefore, hazy skies and limited
rainfall activity is expected across the islands in general. Normal
to above normal temperatures will continue each day, especially
across the lower elevations.

.LONG TERM...Saturday through Thursday...

A relatively strong tropical wave is expected to impact the region
on Saturday; though the bulk of the wave itself will remain to the
south of the region, significant moisture advection is anticipated.
Precipitable water levels are forecast to be higher than climate
normals for June over portions of the region, with values of around
1.8 to 2.2 inches. Aloft, however, a mid- to upper-level ridge will
persist through the weekend. The stability associated with this
ridge will inhibit somewhat convective development over the area.
However, with enhanced moisture, there will be sufficient support
for showers and isolated thunderstorms during the afternoon due to
local effects and diurnal heating, especially in northwestern and
interior Puerto Rico. Streamers are also likely to develop,
including the San Juan streamer.

Decreasing moisture is anticipated for Sunday through Monday. Though
the mid- to upper-level ridge is forecast to weaken during this time
frame, its influence will continue, contributing to a less favorable
environment for convective development. That being said, showers are
still likely, with the potential for a few isolated thunderstorms,
during the afternoons, mostly in northwestern and interior Puerto
Rico on Sunday, and western and interior Puerto Rico on Monday.

Gradual increases in moisture are expected to follow on Tuesday,
mostly after midday. Meanwhile, some weak troughing is forecast to
develop at the upper levels over the region and to the west. This
will provide an increasingly favorable environment for development.
Though the instability and moisture increases are relatively modest
on the day, the combination of the two is likely to result in a
noticeable increase in showers and thunderstorms during the
afternoon. Winds are also expected to back somewhat, becoming more
northeasterly/east-northeasterly; as such, the peak in shower
activity is anticipated to be in western and interior Puerto Rico,
extending into southwestern Puerto Rico.

More substantial increases in moisture are anticipated to push into
the region on Wednesday. At this point, though, confidence in the
forecast degrades. There is disagreement between model guidance on
the fate of the mid-level ridge and developing upper-level trough.
Currently, the more likely scenario is for the mid-level ridge to
erode Wednesday into Thursday, with troughing seen over the area,
while the developing upper-level trough is joined and bolstered by
another upper-level low from out of the northwest. As such, the
forecast includes a persisting trend of afternoon shower and
thunderstorm activity for Wednesday. A much drier air mass is
expected for Thursday, however, mitigating the impacts of the more-
favorable-for-development environment aloft, leading to diminishing
shower activity for that day.

&&

.AVIATION...

Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. However, SHRA/TSRA is expected
to develop over western PR btw 18z-22z which may cause tempo MVFR
conds at TJMZ/TJBQ. Low level winds will continue ESE at 10-20 kt
with higher gusts and sea breeze variations after 14z.

&&

.MARINE...

Under the influence of surface high pressure causing tightening
pressure gradients, winds have increased across the area; moderate
to fresh winds will persist over the next several days. These
conditions will also help to sustain the choppy conditions
observed across much of the local waters. Operators of small craft
are also urged to exercise caution. Late this week, a wind surge
is forecast ahead of the arrival of a tropical wave; sustained
winds in excess of 20 knots are possible, and could result in seas
up to 7 feet for the weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 79 91 80 / 30 20 40 40
STT 90 80 88 80 / 20 30 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
459 AM AST Thu Jun 18 2020

.SYNOPSIS...

A generally seasonal pattern continues today, with passing showers
during the overnight and morning hours, and afternoon showers with
isolated thunderstorms in western and interior Puerto Rico, with
streamers forming in the east and off of the USVI. However, a
Saharan Air Layer will bring dust, causing hazy skies tomorrow
into Saturday. Though this will inhibit shower activity, afternoon
showers are still expected for northwestern and interior Puerto
Rico. Saturday brings a tropical wave and more moisture, and
therefore increasing showers. Next week looks to be fairly stable
and dry.

&&

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

A surface high pressure over the central Atlantic will promote
moderate to fresh trade winds across the region through the short
term period. Patches of low-level moisture embedded on this flow
will bring passing showers across the USVI and eastern sections of
PR during the overnight and morning hours. Diurnally induced
afternoon showers with possible thunderstorm development are
expected today mainly over western PR. Elsewhere, streamers are
expected to develop off the islands and move quickly west due to the
breezy trades. A weak mid-level ridge will continue to build north
and over the region during the next several days, this will promote
the trade wind inversion and inhibit vertical development of showers
across the USVI and eastern PR.

Drier air and a Saharan Air Layer will cause hazy skies on Friday
and early Saturday. However, afternoon convection is still expected
over west/northwest PR each day. A tropical wave is forecast to
increase low-level moisture and instability by late Saturday,
increasing the potential for showers and thunderstorm activity
across the region. Normal to above normal temperatures will continue
each day across the islands.

.LONG TERM...Sunday through Friday...

A drying trend is expected to start on Sunday, as the tropical wave
is forecast to leave the region, taking its moisture with it, by mid-
morning. Precipitable water values below seasonal normals are
anticipated, lasting into midweek. Aloft, a persistent mid- to upper-
level ridge will make conditions less favorable for convection as
well.

On Monday, the ridge aloft is forecast to begin to erode at the
upper levels, as the TUTT to the east stretches into the vicinity of
the local islands. An upper-level low is expected to develop on
Tuesday; a weak trough from off of the continent is forecast to
interact with this low, strengthening it, with the resultant trough
shifting westward, placing it more over Hispaniola than our area. As
such, some divergence aloft would be expected with this feature,
persisting as it remains relatively stationary through the end of
the week, which would increase the favorability for convection over
the area. However, moisture is likely to remain a limiting factor
through midweek. An area of moisture is expected to sink southward
toward the area, but remain mostly over the local Atlantic waters,
on Wednesday into Thursday. Additionally, the mid-level ridge is
forecast to remain a prominent feature over the area as well,
especially above 700 hPa, inhibiting any increases in instability.

But, there remains significant uncertainty in the forecast for
midweek next week, most notably with the location and impacts of the
moisture, with disagreement in the model guidance. The GFS has
backed off on the moisture levels as well as how far south it will
reach. In contrast, the ECMWF still favors a wetter solution,
bringing more moisture to the local islands. The forecast reflects a
compromise between these two solutions. This is a relatively weak
feature, and therefore uncertainty is somewhat of a given,
especially a week out, and it will likely be a few days yet until
higher confidence can be ascribed to the forecast for this time
frame. Whether or not the moisture increase materializes across the
local islands, the same general pattern is expected to persist.
Afternoon showers are expected for western and interior Puerto Rico.
A wind shift is expected Tuesday into Wednesday, with winds becoming
more northeasterly, which could lead to some of the shower activity
spreading into the southern and southwestern parts of the island,
where dry conditions have prevailed for some time. If more moisture
reaches the islands, more widespread and stronger showers would be
likely Wednesday.

For Thursday, a dry air mass is expected to precede an approaching
tropical wave. Shower activity will likely be inhibited, though
afternoon showers due to local effects and diurnal heating are still
anticipated in western and interior Puerto Rico, as in the previous
days in this forecast period. And Friday brings a small promise of
change from the dryness of the earlier parts of the week. A tropical
wave will carry enhanced moisture into the area. The upper-level
trough is forecast to still be in place over or just west of the
area, helping to support afternoon shower and thunderstorm
development; as such, an increase in showers is expected, with more
widespread and vigorous activity likely, as well as the potential
for isolated thunderstorms. The main driving factor in where the
rainfall will occur will remain the local effects, and so the peak
in activity would be expected in western and interior Puerto Rico.

&&

.AVIATION...

Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. However, SHRA/TSRA expected
over western PR btw 18z-23z which may cause tempo MVFR conds at
TJBQ. ESE winds at 15-20 kt with higher gusts and sea breeze
variations after 14z.

&&

.MARINE...

Choppy marine conditions persist over the next several days as a
result of moderate to fresh easterly winds across the area. Seas
of up to 5 feet are anticipated, building Friday and through the
weekend to seas of up to 6 feet, due to a wind surge from a
tropical wave. In portions of the local waters, there will be
winds up to around 20 knots today; as such, operators of small
craft are urged to exercise caution.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 79 91 78 / 20 10 30 20
STT 90 80 89 80 / 40 10 30 30

[cycloneye]

 https://twitter.com/TTWeatherCenter/status/1273669497468182531

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
454 AM AST Fri Jun 19 2020

.SYNOPSIS...

Under the influence of a tropical wave passing by the region later
today into tomorrow, increasing shower activity is expected,
starting this afternoon, especially in western and interior Puerto
Rico. Behind this, a Saharan Air Layer follows with generally dry
and hazy conditions for the start of next week.

&&

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

A tropical wave will pass mainly south of the region today, however,
this should increase low level moisture across the local area to
feed afternoon convection between the USVI and eastern PR during the
morning hours and then over western PR during the afternoon.
Isolated thunderstorms are possible across west/northwest PR. Drier
air with a weak Saharan Air Layer(SAL) will filter ahead of the wave
and as it moves through the Caribbean waters, this should result in
fair weather conditions through the morning hours across the
islands. Another area of drier air moves from the east tonight
through Saturday, ahead of another tropical wave that is forecast to
increase the available moisture and therefore rainfall potential
across the islands during the afternoon hours on Saturday. Moisture
associated to this wave lingers through the overnight hours into
Sunday morning. Another SAL will move quickly on Sunday and become
stronger by early next week, this will cause hazy skies across the
region and limit shower activity over the islands. Normal to above
normal temperatures will continue through the short term period.

.LONG TERM...Monday through Saturday...

Drying conditions are expected Monday, and conditions will stay dry
into at least Wednesday; precipitable water values are expected to
be around 1.0 to 1.2 inches Monday and Tuesday, well below normal
for June. A strong Saharan Air Layer will help to maintain the dry
conditions, as well as bringing a significant amount of dust into
the area, leading to hazy conditions. The occasional patch of
moisture carried into the area embedded in the trade winds could
help to support the development of afternoon showers, and isolated
to locally scattered showers are possible in northwestern and
interior Puerto Rico during each afternoon. On Wednesday, moisture
associated with an increasingly disorganized old frontal boundary is
expected to approach the region from the north. There is still
uncertainty with respect to how far to the south this feature will
sink, as well as timing and intensity, however. It seems more likely
that at least a little bit of moisture will be carried into the
area, leading to somewhat increased shower activity. Conditions
aloft will also be more favorable for increased showers, with an
upper level trough forecast to lie somewhat stationary over
Hispaniola for much of next week, providing divergence aloft. Acting
counter to that, however, is a strong mid-level ridge, which will be
the dominant feature through most of next week as well, especially
around and above 500 hPa. Winds are also expected to shift to become
more northeasterly for the midweek. As such, some showers could
extend into the quite dry southwestern portions of Puerto Rico.

Another dry air mass is forecast to make its way into the area
during the day on Thursday. This will inhibit shower activity,
though there remains the potential for showers due to local effects
and diurnal heating in western Puerto Rico during the afternoon.

A more significant shift in conditions is anticipated for Friday
into Saturday. A tropical wave is forecast to push into the region
on Friday, likely after midday, bringing significant moisture to the
area. As such, enhanced shower activity is expected. Passing showers
will be likely during the overnight and morning hours, while
afternoons will see showers with the potential for isolated
thunderstorms, especially in western and interior Puerto Rico.

&&

.AVIATION...

Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. However, SHRA/TSRA expected over
western PR btw 18z-23z which may cause tempo MVFR conds at TJBQ. ESE
winds at 10-20 kt with higher gusts and sea breeze variations after
14z.

&&

.MARINE...

As the tropical wave approaches and makes its way through the
region, increasing winds will continue to contribute to building
seas across most of the local waters. Seas of up to 6 feet are
anticipated at least through the weekend, and winds of up to
around 20 knots are forecast during that time as well. As such,
operators of small craft are urged to exercise caution. There is
also a low to moderate risk of rip currents at the local beaches
today, including Vieques, Culebra, St. Croix, the northern and
southeastern coasts of Puerto Rico.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 92 78 91 80 / 20 10 40 20
STT 90 80 90 80 / 20 10 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
423 AM AST Sat Jun 20 2020

.SYNOPSIS...

A tropical wave is arriving today that will drive scattered
showers across the region. Following the wave, a large plume of
Saharan dust will arrive for Sunday and last into at least mid-
week, with lesser amounts of dust for the rest of the week. Dry
conditions will prevail with this event, with the next tropical
wave projected to arrive next Friday.

&&


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

The remnants of yesterday`s African dust particles combined with the
subsidence ahead of today`s tropical wave will limit shower activity
during the morning hours. Shower activity and the potential for
thunderstorm development is forecast to increase during the
afternoon as the leading edge of the tropical wave reaches the
islands. Therefore, expect warm to hot temperatures across most of
the islands during the morning and early in the afternoon, followed
by convection late in the afternoon and into the nighttime. The
maximum heat indices will range between 102 and 107 degrees
Fahrenheit. The trailing moisture will promote rainfall activity
until at least Sunday morning.

A drying trend will begin by Sunday afternoon after the passage
of the tropical wave. Along with the drier air, a dense Saharan
Air Layer will arrive that should last through the rest of the short
term period. The peak of this dust is forecast for Monday, and
air quality and associated visibilities could be very poor. This
weather pattern will promote above-normal overnight temperatures
(in the low-80s), and thus make it easier to reach high
temperatures in the low to mid-90s each afternoon. Hazy skies will
also prevail Monday and into the long-term.

.LONG TERM...Tuesday through Sunday...

The big story for the long-term forecast will be the continuation
of the Saharan dust event, with more dry weather ahead. The highest
concentrations of dust should peak between Sunday and Wednesday.
However after Wednesday, we will still see moderately hazy air
through the rest of the long-term period.

For the middle of this next week, high pressure will dominate over
the region, resulting in dry conditions. Tuesday specifically looks
very dry with little rainfall expected even for western Puerto Rico
in the afternoon. A bit more moisture will drop in for Wednesday and
Thursday from the north associated with an old front, but with all
the dust in place for Wednesday, minimal rainfall is likely.
Thursday has a better chance though. At upper levels, a trough is
forecasted to develop to our west that will help atmospheric
conditions be more favorable for shower and thunderstorm
development. Though high concentrations of dust can inhibit storm
development, low to moderate amounts may actually help enhance
thunderstorms, and we are still a bit too far out to know how that
might play out.

The best chance for rainfall in the long-term will be on Friday, as
a tropical wave moves into the region. The GFS model has most of the
moisture passing to our south, and the ECMWF has a bit more moisture
moving into the forecast area. However, both models have sufficient
moisture in place for Friday afternoon, and coupled with the upper
level trough, there ought to be some decent rains across the region.
Unfortunately, this does not look like a very impressive tropical
wave and it will likely provide minimal relief to the drought
conditions. Thereafter, conditions are forecasted to become dry once
again for the next weekend.

&&


.AVIATION...

VFR conds will prevail across all terminals thru at least 20/18z.
Then, a tropical wave will bring SHRA/TSRA over the local flying
area after 20/16z. Over the mountain areas are expected the heaviest
activity, where mount obsc and SHRA/TSRA will develop. This may
produce tempo MVFR conds at TJBQ/JSJ especially btwn 20/18-22z.
TIST/ISX will have the potential for SHRA/isol-TSRA. Calm to light
and VRB winds will prevail thru 20/13z, then will return from the E
at 10-20 kt with higher gusts and sea breeze variations.

&&


.MARINE...

With the arrival of a tropical wave today, winds are expected to
increase to around 20 knots and seas will increase up to 6 feet.
Thus, small craft operators are urged to exercise caution. Winds
are expected to be moderate to fresh for most of the next week,
with choppy seas as well. A fairly intense Saharan dust event is
expected to begin on Sunday and last into mid-week. Visibilities
could drop to near 6 miles and possibly even lower. Scattered
showers can be expected today and tomorrow across the local waters
due to the tropical wave.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 92 79 91 79 / 50 60 40 10
STT 91 80 90 81 / 40 50 50 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
438 AM AST Sun Jun 21 2020

.SYNOPSIS...

The big story for the next several days will the dense Saharan
dust event. Along with the dust, dry air will lead to fairly calm
weather for the next several days. The next tropical wave is
expected to arrive Thursday night. Marine conditions will be
choppy due to moderate to fresh easterly winds associated with the
tropical wave leaving the region today and a fairly strong
surface high in the central to east Atlantic.

&&


.SHORT TERM...Today through Tuesday...

A drying trend will continue as the lingering moisture of
yesterday`s tropical wave exits the region. A dense air mass with
suspended African dust particles will create hazy skies and poor
visibilities across the northeast Caribbean through the morning
hours, reaching the U.S. Virgin Islands and Puerto Rico by this
afternoon into the first part of this week. The peak of this event
is forecast between late tonight and early Monday, lasting until at
least mid-week. This weather pattern will promote above-normal
overnight temperatures (in the low-80s), making it easier to reach
high temperatures in the low to mid-90s each afternoon.

.LONG TERM...Wednesday through Monday...

By Wednesday, the worst of the dust should be behind us, though
moderate amounts of dust are expected for the full duration of the
long-term period. Some moisture will drop in for Wednesday and
Thursday from the north associated with an old front. The moisture
does not look like much at this point, but showers should be able to
develop over southwest PR under northeasterly flow for Wednesday,
though these showers will likely be unimpressive. Thursday however
looks better for showers and thunderstorm development. A trough at
upper levels is still expected to develop to our west, that will
enhance shower and thunderstorm activity. With winds switching more
from the southeast, winds will converge over the northwestern
portion of PR in the afternoon, so that is where the activity should
be.

Friday looks even more interesting as a tropical wave is expected to
move through the area, and may also be enhanced by the upper-
level trough to the west. The GFS model is projecting a more
robust wave compared to yesterday, but the European model has a
less impressive wave than what it was simulating yesterday with
most of the moisture exiting the region by Friday afternoon. With
still plenty of time before its arrival, more changes to the
forecast of this wave are probable. Thereafter however, dry
conditions are once again expected to prevail through the weekend
and into the next week with only weak patches of moisture riding
in on the easterly trade winds.

&&


.AVIATION...

VFR conditions will prevailed. However, a dense Saharan air mass
will reduce VIS after 21/18z across the local flying area between 6-
9 SM and diminishing overnight into Monday. Calm to light and VRB
winds will prevail thru 21/13z, then will return from the ESE at 10-
20 kt with higher gusts and sea breeze variations.

&&


.MARINE...

Moderate to fresh winds will continue for the next several days,
leading to choppy seas up to 5 to 6 feet. At this point, it
appears Small Craft Advisory conditions may be met for Monday
night and into Tuesday due to the windy conditions, and the
decision to put that advisory out will be made in the next 24
hours. Regardless, small craft operators are urged to exercise
caution. Finally, expect lower visibility due to Saharan dust.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 92 79 91 80 / 20 20 20 20
STT 92 82 91 80 / 20 20 10 20