Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
Issued by National Weather Service Miami FL
327 AM AST Sat Jan 11 2020


SHORT TERM...Today through Sunday Night...
Expect current broad high pressure system north of the region to
continue its dominance over the local weather conditions through
the rest of the weekend. As a result, the southern periphery of
the high will keep Puerto Rico and the United States Virgin
Islands under a steady trade wind regime, with tight pressure
gradients bringing periods of gusty winds, possibly into gale
intensity at times.

Latest model solutions suggest the presence of a 35-40kt low
level jet across the region, which will combine with the robust
easterly trades to generate passing showers, and although most
should remain shallow and rather quick, some of the larger showers
could produce strong wind gusts.

LONG TERM...Monday through Friday...
Latest global models keep broad sfc ridging in place across the
west Atlantic, with generally breezy conditions prevailing through
the middle of the work week. Expect periods of wind gusts,
possibly reaching 25 to 30 mph at times, along with continuing
moisture advection and passing showers through the middle of the
work week. The upside of this synoptic scenario is that most
showers should move fast enough for rain accumulations to remain
low. Although, a couple of localized heavy downpours can not be
ruled out.

Long range guidance show an approaching mid level trough, which
erodes as displaces the aforementioned ridge during the first half
of the work week. It also pulls a weakening cold front boundary
closer to Puerto Rico in the Tuesday-Wednesday time frame. But
the influence of this trough is short-lived as the mid-level ridge
is expected to re-establish across the region by Wednesday
afternoon. But VIL and PWAT model values suggests that enough
added moisture from the trough should be available for a modest
increase in showers, with late Monday into Wednesday being the
most active.

By Thursday, moisture decreases as drier air filters into the
region. But enough leftover moistUre will linger over Puerto Rico
and the US Virgin islands for at least scattered showers to keep
developing each afternoon and evening.

&&

.MARINE... Strong and gusty trades continue through early next
week, with Small Craft Advisories in effect. Marine conditions
will continue to deteriorate during the next few days with seas
increasing up to 14 feet by Saturday. Also, elevated risk of rip
currents can also be expected for most beaches in Puerto Rico,
Vieques, Culebra, Saint Thomas, Saint John, and Saint Croix
through the weekend into next week.

&&

.AVIATION...VFR should prevail at all terminals with periods of
gusty trades in the 30kt range. Fast- moving easterly showers may
bring brief bouts of sub-VFR conditions over the terminals at
times.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 74 83 75 / 50 50 50 50
STT 85 78 84 78 / 50 50 50 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
524 AM AST Sun Jan 12 2020

.SYNOPSIS...

A strong Bermuda high pressure to the north of the region will
continue to promote strong winds throughout the area. These
enhanced trade winds will carry passing showers across the local
islands and waters through the first half of the week; patches of
moisture embedded in the trades will also aid in the development
of afternoon showers, and conditions aloft will become more
favorable for convection tomorrow night. Hazardous marine
conditions brought on by these stronger winds will also continue
into midweek in all local waters.

&&

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

Strong Bermudas high pressure yields windy easterlies across the
northeast Caribbean, which are bringing frequent patches of moisture
with clouds and showers across Puerto Rico and the U.S. Virgin
Islands. This feature will continue to dominate the local weather
until at least Monday evening. The western half of Puerto Rico can
expect clear skies during the evening and early morning hours,
but diurnal heating and orographic effects will induce afternoon
showers each day.

The weather panorama will change late Monday night into Tuesday, as
an inverted mid- to upper-level trough is forecast to amplify from
the eastern Atlantic over the islands. This weather pattern will
present a better chance for the formation of thunderstorm activity.

Hazardous coastal conditions continues across the U.S. Virgin
Islands and Puerto Rico. Therefore, beachgoers should monitor the
Coastal Hazard Message (CFWSJU) text product for additional
information.

.LONG TERM...Wednesday through Sunday...

A strong zonal ridge persists across the Atlantic on Wednesday,
allowing for a continuation of the enhanced trade winds that we have
been seeing across the region as we head into this new week. As the
ridge weakens and pulls away to the east Wednesday into Thursday,
winds will begin to gradually subside over the area. By late
Thursday, wind speeds will be closer to normal levels for the area,
around 10 to 20 knots. However, another ridge pushing off the coast
of the mainland US will likely see another increase in winds for the
end of the week.

There will remain an area of deep, enhanced moisture associated with
a weak disturbance over the area on Wednesday. Aloft, an upper-level
trough is expected to lie to the east/northeast of the area, having
exited the region, while a mid-level ridge builds over the forecast
region from the northwest. These features will favor increasing
stability aloft, limiting significant development, though an
isolated thunderstorm or two cannot be ruled out. Passing showers
are expected in the morning and overnight, while local effects and
daytime heating will cause afternoon showers over portions of the
local islands, especially western and interior Puerto Rico.

Late on Wednesday, moisture aloft will diminish as the easterly
disturbance pulls away from the area. Lingering moisture will remain
over the area on Thursday, but is expected to largely be constrained
to the lower levels of the atmosphere. As such, decreasing shower
activity is expected for the second half of the work week. Passing
showers are anticipated for the overnight and morning hours, with
afternoon showers developing, especially in western portions of
Puerto Rico, due to diurnal heating and local effects. Rainfall
amounts are currently not expected to be significant. By the
weekend, somewhat drier air will push in place over the region.
Patches of moisture embedded in the trade winds will be sufficient
to support isolated to scattered passing showers and afternoon
showers, though.

&&

.AVIATION...

Mainly VFR conditions are expected to continue through the forecast
period. Winds will be out of the E-ENE at 10 to 15 knots, increasing
between 15 and 25 kt with gusts around 35 kt aft 12/13z. Under this
wind flow, occasional quick-moving passing SHRA/+SHRA and clouds
could momentarily lower ceiling and VIS at TAF sites.

&&

.MARINE...

Strong winds across the local waters continue to generate hazardous
marine conditions. A gale warning remains in place over the outer
Atlantic waters into this afternoon, with small craft advisories for
all other marine zones. The small craft advisories are in effect
into Wednesday morning. Additionally, there remains a high risk of
rip currents across the local beaches, and high surf advisories
remain in place through Wednesday as well for northwestern to
northeastern Puerto Rico, and Vieques, Culebra, and St. Croix.
Though improving conditions are expected during the midweek,
hazardous seas look quite likely to last into the second half of the
week.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 74 82 71 / 80 70 50 60
STT 84 73 84 72 / 50 40 60 60

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
506 AM AST Mon Jan 13 2020

.SYNOPSIS...A strong surface high pressure anchored over the north
Atlantic will continue to generate windy conditions across the
region. Under this flow, scattered showers will are forecast to move
in from the waters with brief periods of moderate to locally
heavy rain. Windy conditions are also generating hazardous marine
conditions, which are expected to last through at least midweek.
As a result, Small Craft and High Surf Advisories, as well as a
High Rip Current Risk are in effect. Relatively drier weather
conditions, as well as improved marine conditions, are expected
by Thursday and continuing through early next week.


&&

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

Strong SFC high pressure across the western Atlantic will continue
to cause a tight pressure gradient across the local area. Therefore
windy conditions are expected to continue through the first half of
the workweek. With these winds, scattered quick moving showers will
affect the local area today, but an increase in moisture and shower
activity is expected late tonight and through Tuesday. This is due
to an inverted mid to upper level trough that will be over the local
area. There is also an increase in moisture expected on Tuesday,
continuing into Wednesday, which will help in causing an increase in
shower activity and possible thunderstorms due to the aforementioned
mid to upper level trough, especially for Tuesday.

Even though the WRF model solution has significant amounts of rain
forecast for Wednesday, the rainfall max is forecast across central
PR which is not in agreement with the GFS model, plus the WRF POP
forecast seems low and inconsistent with the overall synoptic
pattern, especially when considering the amounts of rain it is
forecasting, for that reason we lowered the POPs for Wednesday and
went more with pops in the 40s to account for uncertainty, we will
adjust as things become more clear later today. Actually, we decided
to cap the POPs at 70% with numerous showers and isolated
thunderstorms in the short term forecast, down from what we
inherited, but not as much as WRF POP forecast suggested. That said,
it is likely that we observe rain in most locations of the forecast
area over the next few days, but having such a high probability of
rain in the forecast with little rainfall accumulation may be
misleading to the actual expected weather, which is scattered to
numerous showers, mostly brief with pauses between showers. The
bottom line is, that we do expect rain, and even more on Tuesday and
possibly into Wednesday, but we do not expect continuous rain
without pause, instead we expect passing showers, some of which
could be moderate to heavy over brief periods of time.

With regards to the winds, the breezy to windy conditions are still
expected through at least Wednesday. However, the latest guidance
suggested lighter winds compared to the previous model run. In
addition, the inherited winds and wind gusts were higher than what
was being observed, for that reason we used the latest guidance and
made adjustments in order to have them match with the current
observed winds. For that reason, the wind gusts in the forecast
could be up to 35 MPH or up to around 32 knots over the waters, and
although some instances of 34 knot or higher wind gusts are
expected, it would not be frequent enough to meet Gale Warning
criteria over the local waters, and therefore we decided to keep the
Small Craft Advisory with sustained winds up to around 25-27 knots
and occasional gusts.


.LONG TERM...Thursday through Monday...

Recent model guidance calls for relatively drier conditions during
the long-term forecast period. Although a few patches of low-level
moisture may still move across the region from time-to-time,
significant shower activity nor rainfall accumulations are
expected. This conditions will be supported by unfavorable
conditions aloft due to the influence of the subsidence side of
an upper-level trough moving east-northeast of the forecast area,
followed by a developing mid-level ridge moving into the area
from the northwest. Nevertheless, overnight and early morning trade
wind showers are expected to affect portions of eastern Puerto
Rico and the US Virgin Islands, while limited afternoon convection
is still expected to affect portions of the interior and western
Puerto Rico each day. In terms of winds, fresh easterly winds
between 15-20 knots are expected on Thursday, but another surface
high pressure moving off the eastern coast of the United States
into the western Atlantic will cause wind to turn from the
northeast and increase between Friday and Saturday. As the
aforementioned high continues to move eastward into the central
north Atlantic, winds are expected to shift back to the east by
Sunday into Monday.


&&

.AVIATION...Mainly VFR conditions are expected through the forecast period, with
VCSH across the local terminals. Winds will be from the ENE at 15 to
20 knots, increasing between 15 and 25 kt with gusts up to around 35
kt after 13/12Z. The brief SHRA activity expected across the local
area may cause brief moments of lower CIGS and VIS a swell as
gusty winds as the SHRA pass through or near the local terminals.


&&

.MARINE...A strong surface high pressure continues to promote
strong wind between 20-30 knots with higher gusts across the
region, resulting in hazardous marine conditions that will last
through at least midweek. Therefore, Small Craft Advisories
continue in effect for seas up to 14 feet for most of the local
waters. There is a high risk of rip currents for most beaches of
Puerto Rico and the US Virgin Islands, and a High Surf Advisory
for beaches along the northwest to northeast coast of Puerto Rico,
Culebra, Vieques and Saint Croix.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 83 72 81 73 / 60 70 70 50
STT 84 71 84 73 / 60 70 60 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
530 AM AST Wed Jan 15 2020

.SYNOPSIS...A strong surface high pressure drifting across the
north Atlantic and north of the region continues to generate a
fresh to strong easterly wind flow across the forecast area. Under
this flow, scattered to locally numerous showers and isolated
thunderstorms will continue to affect the local islands. These
conditions are also generating hazardous marine conditions. Although
these conditions are forecast to improve by Thursday afternoon,
hazardous seas are expected once again with the arrival of another
swell during the weekend. The entrance of relatively drier air
will support tranquil weather conditions, as well as elevated to
critical fire weather condition, by the end of the workweek and
continuing through early next week.


&&

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

Strong SFC high pressure north of the local area will continue to
cause a tight pressure gradient across the local area, but the
gradient will be gradually relaxing later today into Thursday and
Friday. Therefore windy conditions are expected to continue today,
but slightly less windy by tonight, as winds gradually decrease this
second half of the workweek. There is still an inverted upper trough
that could promote isolated thunderstorms in the area today, but
this too is weakening and the thunderstorm potential greatly
diminishes after today. Higher than normal moisture is expected this
morning and early afternoon, drier air is expected to start moving
in by tonight, becoming even drier on Thursday and Friday.
Therefore, the peak timing for significant rainfall is expected to be
this morning and early afternoon. The areas that are expected to be
most affected are the north and eastern sections of PR and the USVI.
However, there is a chance of showers across w-sw PR in the
afternoon, but it would be mainly limited to portions in the higher
elevations, not as much in the coastal areas, there is only a slight
chance of significant rainfall across the south and southwest
coastal plains. Overall, for Thursday and Friday the showers
activity is expected to diminish significantly as the much drier air
moves in. The daytime high temperatures are expected to be in the
low to mid 80s across the lower elevations, with the S-SW portions
of PR mostly in the 85-88 degree range and in the 82-85 degree range
elsewhere in the lower elevations in PR and across the USVI. Temps
in the mid 70s to low 80s across the higher elevations.


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

Although patches of low-level moisture, mostly associated to the
remnants of a old frontal boundary, are expected to move in from
time- to- time, model guidance continues to support relatively
drier conditions during most of the long-term forecast period.
These conditions are the result of expected unfavorable conditions
aloft with the dominance of a developing mid-level ridge moving
in from the northwest by Saturday and holding over the region
through early next week. Nevertheless, there is a chance for overnight
and early morning trade wind showers moving over portions of
eastern Puerto Rico and the US Virgin Islands. Then, limited
afternoon convection is still expected over portions of the
interior and western Puerto Rico each day. A slight increase in
the frequency and areal coverage of showers is possible on Sunday
and Monday with increase low-level convergence. At the surface,
winds are expected to turn from the east and hold around 10-20
knots as a surface high pressure moves across the western Atlantic
and north of the region. However, as the aforementioned feature
drifts eastward into the central north Atlantic, winds are
expected to turn from the east-southeast by Monday. By Tuesday and
continuing on Wednesday, a surface trough is expected to approach
the area from the northwest, causing a saddle over the area with winds
diminishing and shifting more from the south-southeast. This will
also lead to an increase in daytime high temperatures and the risk
for wildfires.


&&

.AVIATION...SHRA/TSRA expected over the local flying area,
especially through 15/16Z, which will cause moments of MVFR conds
across TIST and TJSJ, and possibly brief at TISX. TEMPO groups in
TAF will be issued as confidence in timing increases. Winds will
remain from the ENE at 10 to 20 knots, with gusts up to around 25-30
kt, especially near SHRA/TSRA. After 15/16Z, SHRA will increase
across W-PR, so TJMZ could observe VCSH, elsewhere, the local
weather is expected to gradually improve.


&&

.MARINE...Although conditions are slowly improving, a strong
surface high pressure continues to promote a fresh to strong
easterly wind flow ranging between 15-20 knots with higher gusts
across the region, resulting in hazardous marine conditions. As a
result, Small Craft Advisories remain in effect for seas up to 10
feet. In addition, there is a high risk of rip currents for most
beaches along the northwest eastward to southeastern coast of
Puerto Rico, as well as beaches along the south coast of Vieques,
northeast coast of Culebra and most beaches of St. Croix.


&&

.FIRE...Although shower activity is expected to affect Puerto
Rico, limited shower activity is expected the Southern Plains
today, particularly across south central to southwestern sections
of the island today. The forecast calls for relative humidity
values to drop into the low to mid 50s, and even into the upper
40s once the morning shower activity dissipates. In addition, recent
KBDI and 10-hour moisture content observations support a drying
pattern with values between 530-600 and 8-10%, respectively.
Daytime high temperatures are forecast to peak into the mid 80s
under a fresh to strong easterly wind flow ranging between 15-20
mph with higher gusts and sea breeze variations. The combination
of these conditions will result in elevated fire weather
conditions across these areas. These conditions may persist during
the next few days as relatively drier air dominates the local
conditions.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 71 85 73 / 80 40 40 40
STT 84 72 83 72 / 60 30 30 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
457 AM AST Thu Jan 16 2020

.SYNOPSIS...A surface high pressure over the north Atlantic
continues to generate a fresh to strong easterly wind flow across
the forecast area. Under this flow, drier air is expected to move
in and bring relative fair weather conditions today and on
Friday, as well as elevated fire weather conditions. However, a
relatively wet pattern is expected during the rest of the forecast
period with a gradual increase in the frequency, intensity and
areal coverage of showers starting on Saturday and continuing
next week. This will be the result of the remnants of an old
frontal boundary moving across the region during the weekend,
followed by a deep trough stalling over the area through most of
next week.


&&

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

Drier air is moving in and it is expected to prevail through Friday
with the exception of a patch of slightly higher moisture on
Thursday night. This drier air is forecast to have precipitable
water values of around an inch or less for much of Today and Friday,
which is below the 25th percentile of normal. Therefore much drier
weather is expected today and Friday, but scattered showers are
expected tonight with the brief patch of moisture. In this case the
available guidance was in good agreement with very low POPs through
today and Friday, and then again the peak tonight. The showers that
are expected tonight are mainly expected across northeastern Puerto
Rico, the Atlantic waters and the northern USVI. There is a slight
chance of showers across SW-PR this afternoon but the activity is
expected to be brief. Otherwise fair weather is expected with
perhaps a few light and isolated showers that would cause little to
no rainfall accumulations, and most of those would be occurring over
the waters. So the bottom line is that the weather is expected to
improve and much less shower activity is expected, and even those
showers that are observed are not expected to cause hazardous
amounts of rain today or Friday.

However, for Saturday, the available moisture and shower activity is
expected to increase as a frontal boundary moves in from the north.
The precipitable water jumps up to around 1.25 to 1.4 inches on
Saturday morning, before decreasing once again in the afternoon to
under an inch but then increasing to about 1.25 inches on Saturday
evening. Therfore scattered showers are expected across the local
waters, eastern PR and the USVI as the available moisture moves
closer to the normal levels for this time of year.

The local winds are decreasing, and are expected be much lighter for
this latter part of the week than it had been for the past several
days. Moderate winds from the east northeast are expected to remain
at around 15 mph during the daytime hours, decreasing overnight to 5-
10 mph across land areas. The daytime temperatures are expected to
be near normal, with highs in the low to mid 80s across the lower
elevations and in the 70s across the higher elevations for the next
couple of days.

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

Recent model guidance no longer supports a drier weather pattern
during the long-term forecast period. These guidance now calls for
the remnants of an old frontal boundary, steered by a surface high
pressure over across the western Atlantic, to continue moving into
the region under a generally east-northeast wind flow on Sunday.
Although favorable conditions aloft are not expected due to the
presence of a mid- level ridge, shallow shower activity is still
expected with these patches of low-level moisture. By Monday,
winds are expected to shift from the east-southeast and then
gradually from the south-southeast on Tuesday as a surface
induced trough approaches the region from the north- northwest
and stalls over the northeastern Caribbean through the rest of the
workweek. In the meantime, a strong mid-to upper level trough
will push the mid- level ridge eastward into the central Atlantic
and away from the region by midweek. These events will result in
favorable conditions to support an increase in low- level
moisture convergence and the chance for deeper shower activity.
Model guidance also calls for a weak surface low to develop over
the northeastern Caribbean by the end of the forecast period,
providing additional instability to support an increase in the
frequency and areal coverage of showers across the forecast area.
Under the south to southeast flow, above-normal temperatures are
also expected with daytime high temperatures possibly reaching the
low 90s across coastal areas.


&&

.AVIATION...VFR conds expected across the local terminals for the
next 24 hours. There is a chance of VCSH at TJMZ after 16/18Z and
for TIST and TJSJ after 16/20Z as ISOL/SCT SHRA could be observed
across the area, otherwise fair weather is expected. Winds will be
generally between 5 and 10 kts through 16/13Z, increasing thereafter
up to 15 kts with occasional gusts from the east to east
northeast.


&&

.MARINE...Although marine conditions are expected to improve
throughout the day today, hazardous seas and fresh to strong
winds are expected through early this afternoon. Therefore, Small
Craft Advisories continue in effect for seas up to 7 feet and
winds up to 20 knots. In waters where small craft advisory are
not in effect, small craft operators are urged to exercise caution
due to seas up to 6 feet. There is a high risk of rip currents
for beaches along the northwest to northeast coast of Puerto Rico,
north and east coast of Culebra, and most beaches in Saint Croix. Relatively
tranquil marine and coastal conditions will hold through at least Friday,
but another northerly swell and wind-driven seas will generate
hazardous seas and dangerous rip currents during the weekend and
continuing through early next week.

&&

.FIRE...Limited shower activity is expected across the forecast area
today, reducing the chance for wetting rains across the region,
particularly across the southern plains of Puerto Rico. KBDI
observations continue to support a drying pattern with an
increasing trend ranging between 530-610, while 10-hour fuel
moisture values have remain consistently between 9-12%. Relative
humidity is forecast to drop in the low to mid 50s, and possible
briefly dropping into the mid to upper 40s during the late
morning and early afternoon hours. Daytime high temperatures are
forecast to reach the mid 80s under a fresh easterly wind flow
peaking around 15 mph with higher gusts and sea breeze variations.
The combination of these conditions will result in elevated fire
weather conditions, especially across the southern coastal plains
of Puerto Rico. These conditions may persist during the next few
days as relatively drier air with limited shower activity dominates
the region.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 83 72 83 74 / 30 30 20 40
STT 84 71 83 73 / 20 20 20 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
521 AM AST Fri Jan 17 2020

.SYNOPSIS...A surface high pressure over the north Atlantic
will promote a moderate easterly wind flow across the forecast
area today, but winds are expected to increase as another surface
high pressure builds across the western Atlantic during the
weekend. Although drier air will support fair weather conditions
today, the remnants of an old frontal boundary will increase the
chance for showers tonight into the weekend. A relatively wet
weather pattern is expected through most of next week as a
surface induced trough crosses the region by midweek and the
remnants of another frontal boundary are steered into the area by
the end of the workweek under favorable conditions aloft.


&&

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

The drier than normal moisture will prevail today across the local
area, but little patches of moisture will start moving in tonight
into Saturday as a frontal boundary approaches the local area for
Sunday. That said, the precipitable water values are not forecast to
be above normal from now through Sunday, it will simply go from much
below normal today to near normal on Sunday, with precipitable water
values at around 0.9 inches this morning to about 1.35 inches on
Sunday. This means that little to no shower activity is expected for
most of the day today, although there is a chance of locally induced
showers across the SW sections of PR this afternoon, but scattered
shower activity is expected to make a return to the local area,
mainly the Atlantic waters, north and eastern PR and the northern
USVI tonight as moisture increases. These sections of the forecast
area are expected to have scattered shower activity through Saturday
as the front keeps pushing through from the north, causing also the
Caribbean waters and Saint Croix island to observe scattered shower
activity on Saturday and Sunday. Most of this shower activity is
expected to be relatively light, but moderate across isolated areas,
which could cause ponding of water on roadways and poor drainage
areas.

There is also an increase in wind speeds that are expected this
weekend. A surface high pressure will move into the western Atlantic
and north of the local islands, which will tighten the pressure
gradient, causing breeze conditions to gradually start on Saturday.
Although not as breezy as the event we had a few days ago, it will
be significant enough to cause hazardous marine conditions and for
the sea breeze to not develop across western PR since there will be
a good NE wind at around 15-20 mph from Saturday into Sunday. As far
as temperatures go, the daytime high temps today will be in the mod
80s across the low elevations of PR and across the USVI, and in the
mid to upper 70s across the higher elevations of PR, slightly
cooler, about 1-3 degrees cooler on Saturday.

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

Recent model guidance continues to support a relatively wet
weather pattern during the long-term forecast period with
an increasing pattern of shower frequency and areal coverage as
the week progresses. As a surface high pressure continue to move
eastward across the north Atlantic, the remnants of an old frontal
boundary, enhanced by low-level convergence, will continue to
move into the region under an east to southeast wind flow.
Intermittent patches of moisture will cause precipitable water
values to peak around 1.5 inches on Monday. Although favorable
conditions aloft are not expected due to the presence of a mid-
level ridge, shallow shower activity is expected to affect the
area. Between Tuesday and Wednesday, a surface induce trough is
forecast to approach and cross the region from the northwest. In
the meantime, a strong mid-to upper level trough will push the
mid-level ridge eastward into the central Atlantic and away from
the region by midweek. These events will lead to an increase in
shower activity due to favorable conditions aloft and an increase
in instability and low-level convergence. As the surface trough
tilts eastward with its axis extending into the northeastern
Caribbean, a saddle will develop over the area causing winds to
diminish and become variable by late Wednesday night into
Thursday. Thereafter, another surface high pressure moving across
the western Atlantic will cause winds to turn from the northeast,
steering the remnants of another frontal boundary and trailing
moisture from the aforementioned trough into the region through
the end of the workweek.


&&

.AVIATION...VFR conds expected across the local terminals for the
next 24 hours. There is a chance of VCSH at TJMZ after 17/18Z and
for TIST and TJSJ overnight tonight after 18/00Z as ISOL/SCT SHRA
could be observed across the area, otherwise fair weather is
expected. Winds will be generally between 5 and 10 kts through
17/13Z, increasing thereafter to 10-15 kts with occasional gusts
from the east to east northeast with sea breeze variations.


&&

.MARINE...Although marine conditions have improved, small craft
operators are urged to exercise caution across most of the local
waters due to choppy seas up to 6 feet. These conditions will hold
through late Friday night, but another northerly swell and wind-
driven seas will generate hazardous marine conditions during the
weekend into early next week. As a result, Small Craft Advisories
will be in effect starting on Saturday morning. There is a
moderate risk of rip currents for beaches along the north coast
of Puerto Rico, as well as most beaches in Vieques, Culebra, and
the US Virgin Islands. The risk will elevate to high as marine
conditions deteriorate on Saturday.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 82 72 / 20 40 40 40
STT 85 76 84 75 / 10 30 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
440 AM AST Sat Jan 18 2020

.SYNOPSIS...

A ridge of high pressure will create stable weather conditions
over the local area through Monday. Then a weak frontal boundary
will cause the surface ridge to weaken, as well as increase low-
level moisture and instability over the region. This will lead to
frequent passing showers over Puerto Rico and the U.S. Virgin
Islands. Another frontal boundary is expected to move across the
region during the end of the workweek, and persist through the
weekend.

&&

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

Mid to upper level high pressure ridge will continue to build and
spread across the region through the weekend into Monday. This
will maintain overall dry and stable conditions aloft. Strong
surface high pressure ridge will enter and spread eastward across
the west and southwest Atlantic. This will tightening the local
pressure gradient beginning later today and continuing through
Sunday. Consequently increasing east to northeast trade winds can
be expected. The building high pressure ridge north of the region
and the increasing moderate to strong northeast trade winds will
push remnants of a frontal boundary across the region today
through Sunday. This added moisture will favor a better chance for
the development of early morning showers along the north and east
coastal areas of the islands...as well as locally and diurnally
induced afternoon showers mainly over parts of the central
interior and extreme southwest sections of Puerto Rico. However,
with the increasing winds expected, afternoon shower activity will
be of fast moving and therefore no significant accumulations are
forecast at this time.

By late Sunday through Monday expect the prevailing winds to again
become more easterly. This will result in a return of late evening
and early morning trade wind shower activity to portions of the
local waters and coastal sections of the islands. By Monday
afternoon, lingering moisture along with local and diurnal effects
will support mostly isolated to scattered showers over parts of the
west and northwest sections of the islands. No significant rainfall
accumulations or flood problems are forecast during the period.
Breezy and gusty conditions are however expected later today through
at least Sunday.

&&

.LONG TERM...

The long-term period looks unsettled as a result of several weak
frontal boundaries, which will move across the U.S. Virgin
Islands and Puerto Rico. The frontal boundaries will increase low-
level moisture and instability; this will lead to the development
of frequent passing showers.

Tuesday through Wednesday, a surface ridge is progged to slide
northeast ahead of an intensifying mid to upper-level trough over
the western Atlantic. The shift in the surface to the mid-level
ridge will result in low-level convergence and weak upper-level
divergence across the region. Also, guidance shows a robust low-
level jet with winds ranging from 60 to 90 kts persisting across
the region through the end of the week. The above conditions,
combined with weak troughiness aloft, increasing instability and
moisture will result in unsettled weather conditions. Therefore,
expected continuous showers to move across Puerto Rico and the
U.S. Virgin Islands during the middle of the week.

Thursday, an area of high pressure is expected to move off the
eastern seaboard, this will cause the surface ridge to abate over
the region as the frontal boundary strengthens over the Atlantic
waters. A cyclonic col is forecast to develop over the region,
and this will cause winds to slow and allow moisture to pull over
the area from the north/southeast.

Friday, the GFS shows the front boundary across Puerto Rico during
the afternoon. The frontal boundary and northerly winds will aid in
the development of showers across most of the region on Friday.

Saturday, the GFS shows the boundary draped across the U.S. Virgin
Islands and Puerto Rico through the afternoon, before moving the
boundary south of the area late Saturday night into Sunday morning.

&&

.AVIATION...

VFR at all terminals durg prd. Quick passing SHRA in
prevailing NE winds flow ovr Atl waters and local passages as .
well as in route btw islands. Sct ocnl BKn lyrs nr FL025...FL040.
VCSH at TJSJ/TJBQ/TIST/TISX as well as TNCM/TKPK til 18/14z. Sfc wnd
fm ENE less than 10 kt...increasing 10-20 knots with gusty winds and
sea breeze variations after 18/14z. No sig AVN wx impacts attm.

&&

.MARINE...

A northerly swell, as well as wind-driven seas, will cause hazardous
marine conditions through early next week. Also, frequent passing
showers with gusty winds are expected to move across the local and
region waters over the next several days. A small craft advisory
is in effect for the Atlantic waters this morning, with the small
craft advisory conditions expected across the Caribbean, Mona
Passage, and the northern near-shore waters of Puerto Rico later
this afternoon. Seas will range from 6 to 8 feet with seas
occasionally reaching 11 feet. There is a high risk of rip
currents for the northern and eastern beaches of Puerto Rico
today.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 82 71 84 73 / 50 70 60 40
STT 84 74 85 76 / 40 70 40 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
506 AM AST Sun Jan 19 2020

.SYNOPSIS...

Hazardous marine conditions will continue across the outer and
near-shore waters through early next week. These conditions are
occurring due to a northerly swell and wind-driven waves over the
Atlantic waters. A polar trough is forecast to move into the
Atlantic waters early next week, and cause the surface high to
weaken and move northeast of the area. The weakening of the
surface high will turn the surface winds in a southerly direction.
Also, shallow moisture ahead of the front will cause frequent
passing showers and gusty winds over the region. The front is
expected to move over the area on Thursday before moving south of
Puerto Rico late next week into the weekend.

&&

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

Strong Mid to upper level high pressure ridge will hold across the
region through Monday, then gradually weaken by Tuesday as a polar
trough will sweep across the western Atlantic. This will maintain
overall dry and stable conditions in the mid to upper levels with
only shallow moisture expected to be tapped below the strong trade
wind cap inversion. Surface high pressure ridge will continue to
shift eastward into the central Atlantic today through Monday as a
cold front will enter and move across the western Atlantic. This
pattern will slowly relax the local pressure gradient leading to a
decrease in the now moderate to strong east to northeast trades by
Monday and Tuesday, when winds are then expected to become more
southeasterly.

In the meantime the fairly strong east northeast low level winds
will continue to push the band of shallow moisture along a frontal
boundary southwards across the forecast area today through Monday.
This added moisture will favor shower development across the islands
and coastal waters today. Periods of passing showers can therefore
be expected to affect the north and east coastal areas of most of
the islands though the early morning hours today. During the
afternoon hours, locally and diurnally induced afternoon showers can
be expected over parts of the interior and west to southwest
sections of Puerto Rico, as well as in and around the U.S. Virgin
Islands where lesser shower activity is so far expected during the
morning hours. Afternoon shower activity should again be fast moving
and so far no significant rainfall accumulations are expected across
the islands today.

Later tonight through Monday, expect the prevailing winds to become
more east southeast as the Atlantic high shifts eastwards into the
Central Atlantic. This will result in a return of late evening and
early morning trade wind moisture along with quick passing shower
activity to portions of the local waters and coastal sections of the
islands. By Monday afternoon, lingering moisture along with local
and diurnal effects will support mostly isolated to scattered
showers over parts of the west and northwest sections of the
islands. Rainfall accumulations are so far not expected to be
significant to cause flood problems at this time but ponding of
water on roadways and in poor drainage areas will be likely with the
periods of moderate to locally heavy downpours. Gradual drying trend
expected by Tuesday as winds become more southeasterly and decrease
in intensity. However this will result in slightly above normal high
temperatures at least for Monday and Tuesday.

&&

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

Guidance continues to show an unsettled pattern during the long-term
period as a result of several weak frontal boundaries that is prog
to move over the area. The frontal boundaries will increase low-
level moisture and instability; this will lead to the development of
frequent passing showers as well as gusty winds from time to time.
Also, expected cloudy conditions to prevail during this time.

Wednesday, a surface ridge is expected to move northeast ahead of an
intensifying mid to upper-level trough over the western Atlantic.
The shift in the surface to the mid-level ridge will result in low-
level convergence and weak upper-level divergence across the region.
Guidance continues to put a vigorous low-level jet with winds
ranging from 60 to 90 kts across Puerto Rio and the U.S Virgin
Islands throughout the entire long-term period. The instability
created by veering southerly winds, jet interaction, troughiness
aloft, and increasing moisture will aid in the development of
frequent showers across the region during the afternoon through
late Wednesday. However, the GFS has a precipitable water value of
1.0 inches early Wednesday, and increasing through the day. The
drier air could delay the start of the rain on Wednesday.

Thursday, the GFS shows an area of high pressure moving off the
eastern seaboard into the western Atlantic waters, this will cause
the surface ridge to the northeast of Puerto Rio to continue to
shift away from the area. Also, the frontal boundary to our
northwest will strengthen and move closer to the region. Guidance
shows a pre-frontal boundary move over Puerto Rico Thursday
afternoon. The boundary and its associated moisture will induce
frequent showers across the U.S. Virgin Island and Puerto Rico
throughout the day on Thursday.

Friday, the GFS holds the pre-frontal boundary over the area with
the highest moisture draped across the Caribbean waters.
Nevertheless, frequent passing showers will develop across Puerto
Rio and adjacent Islands.

Saturday and Sunday, the front is progged to move over Puerto Rio
finally. The frontal boundary moving over the area will result in
frequent passing showers over Puerto Rico and adjacent Islands.
Sunday, the frontal boundary is expected to become diffuse and lose
it characteristics. Still, showers are forecast to develop during
the day on Sunday.

&&

.AVIATION...

Prevailing VFR durg prd. The proximity of a frontal
boundary will bring SCT-BKN lyrs nr FL025...FL040...FL070. Ocnl
-SHRA/SHRA ovr local Atlantic waters and en route btw islands
along frontal boundary til 19/14z. Brief MTN top obscr ovr Ern PR
til 19/13z due to SHRA/low CIG. Sfc wnds fm ENE btw 12-20 kt with
hir gusts btw 25-30 kts nr SHRA and along coastal areas. Sfc wnds
bcmg E- NE 15-25 kt with ocnly hir gusts. L/lvl wnds 20-25 kts
blo FL100, then backing and bcmg fm N up to FL250.

&&

.MARINE...

Hazardous marine conditions will continue over the local and
regional waters through early next week. These conditions are
being generated by a wind-driven seas and a northerly swell.
There is a High Surf Advisory and a Coastal Flood Advisory in
effect for the the northern, western and eastern beaches of
Puerto Rico today. Also, a Coastal flood Advisory and High Surf
advisory is in effect for the beaches of Saint Thomas, Saint John
and Adjacent Islands today. For the High Surf Advisory expect
large breaking waves of 8 to 12 feet for the beaches above. There
is a high risk of Rip Currents for all the beaches of Puerto Rico,
Culebra, Vieques, USVI, Saint Thomas and Saint John.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 85 74 / 60 80 60 40
STT 85 76 84 77 / 50 70 70 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
531 AM AST Mon Jan 20 2020

.SYNOPSIS...
Shallow moisture along a frontal boundary will linger across the
region today while slowly decaying. This feature will continue to
bring low to mid level cloud fragments and mostly stratified rains
across the region today through at least early Tuesday. Passing
trade wind showers will continue across the region from time to
time. Surface high pressure north of the region will continue to
shift eastwards farther into the central Atlantic resulting in a
loosening of the local pressure gradient and slowly diminishing east
to southeast trade winds. Cool early morning low temperatures can
be expected with daytime high temperatures expected to be slightly
above normal today and on Tuesday.

&&

.SHORT TERM...Monday through Wednesday... A stationary front
positioned to the south of Puerto Rico is producing stratiform
clouds and precipitation over the region; these showers will
continue to move across Puerto Rico and adjacent Islands today, and
produce light rainfall amounts. TJSJ Skew-T and cross-section
shows moisture trapped between the 1000 to 850 mb level and the
trade inversion through the short-term period. Therefore, expect
occasional showers with partly cloudy skies now through Wednesday.

A Polar trough across the western Atlantic will continue to move
east today through Tuesday; the trough will weaken the mid-level
ridge currently over the area, and cause the surface high pressure
to continue to slide northeast of Puerto Rico. Also, later today, as
the Atlantic high shifts east, surface winds will become east to
southeast across the area. The east to southeast winds will advect
patches of drier air currently in the southern Caribbean and eastern
Atlantic over Puerto Rico and adjacent Islands later today through
Wednesday. The GFS shows precipitable water values falling
throughout the short-term period with the highest total of 1.62
inches today and the lowest total of 1.00 inches during the morning
on Wednesday. The strong inversion in the mid-level of the
atmosphere and limit low-level moisture will cause relatively calm
weather conditions across the region. Nevertheless, showers are
possible across the eastern areas of Puerto Rico and northern
coastal areas during the morning, then over most of the area during
the afternoon due to local and diurnal effects. Also, the southeast
wind flow should slightly increase the daytime high temperatures
over Puerto Rico and adjacent Islands.

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

By Thursday, the surface ridge across the Atlantic is forecast to
shift farther northeast into the central Atlantic, as a cold front
will move into the western and southwest Atlantic and approach
the region. An associated amplifying mid to upper- level polar
trough will also cross the west Atlantic and weaken the ridge now
in place overhead. This will result in a weakening of the trade
wind inversion and promote instability aloft through at least
early Friday. The shift in the surface to the mid- level high
pressure ridge pattern should also result in better low level
moisture pooling and convergence as the frontal boundary is
expected to arrive and sink southwards across the region by the
latter part of the work week. Model guidance also continued to
suggest a vigorous mid to upper level jet max crossing the region
Thursday through Friday. The combination of the instability aloft
and good low level moisture convergence accompanying the frontal
boundary will therefore favor the development of scattered to
numerous to showers with periods of locally heavy rains across the
islands and coastal waters at least through early Friday.

By late Friday and into the weekend, model guidance still suggest
lingering low level moisture but gradually improving and stable
conditions aloft. Therefore expect less frequent early morning
shower activity across the islands and coastal waters. This will
be followed by isolated to scattered showers of short duration
during the afternoon hours. Improving conditions are forecast
by Saturday and through Monday, as the surface high pressure will
once again build and spread across the west Atlantic, resulting
in a more northeasterly wind flow and a stable near normal weather
pattern.

&&

.AVIATION...MVFR are conds are occurring across terminal sites TJSJ,
TISX and TNCM due to SHRA/VCSH which are briefly reducing SFC VSBY.
SHRA/VCSH will continue through 20/15Z for the above areas. Brief
Mtn top obscr ovr E PR due to SHRA/Low CIG. VRF conds elsewhere.
VCSH are possible across terminals TJBQ and TJMZ by 20/16Z with
conds improving by 20/20Z. ESE winds of 15-20 kts with hir gusts
up to 30kt with SHRA. Max winds WNW 50-90 kts btwn FL300-FL450.

&&

.MARINE...Mariners can expect choppy and hazardous seas through
at least Tuesday night. Therefore, small craft advisories are in
effect for the local waters. The combination of a northerly swell
and wind- driven seas will maintain seas up to 12 feet occasionally
higher through at least early Tuesday. Breaking waves between 10
and 14 feet can be expected with this swell action until later
today. Refer to local Surf zone forecast (SRFSJU), Coastal waters
Forecast (CWFSJU), Coastal hazard message (CFWSJU) and Marine
weather message (MWWSJU) for additional information.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 72 88 73 / 60 30 30 30
STT 82 73 81 73 / 50 40 30 30

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
504 AM AST Tue Jan 21 2020

.SYNOPSIS...Remnant moisture along a decaying frontal boundary
will linger across the region during the rest of the morning and
early afternoon hours as winds become more southeasterly. This is
in response to the Atlantic high pressure ridge shifting farther
northeast into the central Atlantic, and a cold front moving
eastwards across the west and southwest Atlantic. Under this wind
flow, the moist low level airmass will be replaced by a drier air
later today through early Wednesday. By Thursday and into Friday
the approach of a cold front and an upper level polar trough will
again destabilize the local environment and increase moisture
convergence across the region. This will increase cloudiness as
well as the enhance for enhanced shower activity. Through at
least early Friday.

&&

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

The frontal boundary, which was positioned over Puerto Rico yesterday,
will continue to lift to the north while decaying today. The high
pressure across the Atlantic lifts to the northeast as a result of
an intensifying polar trough across the western Atlantic. As the
high scurries away, a more southerly wind flow will prevail over
the area. This wind flow will pull pockets of drier air and limited
moisture over Puerto Rico and adjacent Islands. The converging
southerly winds, shallow moisture, upper-level jet, and troughiness
aloft have aided in the development of showers overnight and this
morning. Although, the drier air is forecast to continue to increase
throughout the day and erode the low-level moisture over Puerto
Rico; precipitable water will remain near the 50th percentile for
the month of January through Wednesday. Shower development this
afternoon will be focused near the northern coastal areas of
Puerto Rico as a result of the southerly wind flow. Showers that
develop will be short-lived as a result of the strong inversion in
the mid- levels of the atmosphere.

Wednesday will be a transition day from the relatively drier air
mass to a more moist environment. The polar front continues to
deepen as a result of a potent upper-level jet and jet streaks with
winds of 90 to 115 kts. Moisture ahead of the front will move over
the Atlantic waters during the afternoon. The bulk of the moisture
will advect in from the southwest winds at 850 mb and 700 mb. The
moisture shows when analyzing the relative humidity at 850 and 700
mb. Also, convergence at the surface coupled with increasing
moisture, upper-level instability provided by the upper-level jet
and diffluence aloft could lead to the development of isolated
thunderstorms over the Atlantic waters. The GFS shows 500 mb
temperatures of -7 to -8 degrees Celsius; this is adequate to
support thunderstorms development. Also, TJSJ sounding at 22/18Z has
cape values of 1200 J/kg; this value also supports moderate
instability. Due to the above factors, isolated thunderstorms are
forecast to develop. However, over Puerto Rico and adjacent Islands
at this time isolated to scattered showers are prog to develop. This
activity will be locally and diurnally induced, but also enhanced by
increasing moisture.

Then late Wednesday into early Thursday morning, the GFS brings a
pre-frontal boundary over Puerto Rico, this will destabilize the
atmosphere over the area, and lead to the development of moderate
to heavy rainfall across Puerto Rico and adjacent Islands. The
development of isolated thunderstorms is possible during the
afternoon across Puerto Rico and the adjacent Islands. This
activity could lead minor flooding and ponding of water on
roadways.


.LONG TERM...Friday through Tuesday...
The surface ridge across the Atlantic is forecast to lift farther
northeast into the north central Atlantic, as a cold front will
move across the western Atlantic and sink southwards across the
region. An amplifying mid to upper- level polar trough will also
weaken the ridge aloft resulting in a weakening of the trade wind
inversion leading to unstable conditions aloft through at least
early Friday. The shift in the weather pattern will result good
low level moisture pooling and convergence as the frontal boundary
sink southwards across the region through Friday. Model guidance
remain persistent and suggests a vigorous mid to upper level jet
max crossing the region through early Friday. The combination of
the instability aloft and good low level moisture convergence
will therefore favor the development of scattered to numerous to
showers and possibly isolated thunderstorms with periods of
locally heavy rains across the region until early Friday.

By late Friday and through the weekend, model guidance suggest
lingering low level moisture but gradually improving and stable
conditions aloft with a much drier airmass. Therefore expect less
frequent early morning shower activity across the islands and
coastal waters. This will be followed by isolated to scattered
showers of short duration during the afternoon hours. Improving
conditions are forecast by Sunday and through Tuesday, as the
surface high pressure will once again build and spread across the
Atlantic, resulting in a more east northeast wind flow by Monday
then a more southeasterly on Tuesday.

&&

.AVIATION...VFR are conds are expected drg prd. with SHRA/VCSH over
PR E terminals and USVI through 21/16Z. SHRA/VCSH are forecast to
develop by 21/18Z across terminal sites TJBQ and TJMZ by 21/18Z with
clearing by 22/00Z. ESE winds of 10 to 15 kts with higher gusts. Max
winds WNW 60 to 90 btwn FL 325 to 460.

&&

.MARINE...Mariners can expect choppy and hazardous seas through
at least later this evening. Therefore, small craft advisories
are in effect for the local waters and passages. The combination
of a decaying northerly swell and wind- driven seas will maintain
seas of 8 to 10 feet over the offshore Atlantic and 6 to 8 feet
over the rest of the local waters and passages until later today.
Breaking wave heights between 8 to 10 feet can be expected during
the morning hours along the north coastal beaches, then subsiding
during the afternoon along with the swell action. Refer to local
marine products for additional information. Mariners and beachgoers
should continue to take precautionary measures and remain alert
during the rest of today.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 73 87 74 / 20 40 50 20
STT 82 73 81 75 / 40 40 40 50

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
524 AM AST Wed Jan 22 2020

.SYNOPSIS...An area of moisture is approaching from the east and
southeast, under a light to moderate southeasterly wind flow. This
will bring periods of mostly light early morning over portions of
the south and east coastal areas of the islands. For the rest of
the day afternoon shower activity should be focused over the
northern half of Puerto Rico with lesser amounts expected around
the U.S Virgin Islands. By Thursday increasing moisture and
unstable conditions aloft will favor better chance for increased
cloudiness and shower and isolated thunderstorm development. This
is due to an approaching cold front and a mid to upper level trough
still forecast to move across the forecast area and local Atlantic
waters.

&&

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

Today a few showers are forecast to develop as a result of diurnal,
and orographic effects. The southerly wind flow will keep convection
focused mainly on the eastern and northern areas of Puerto Rico, as
well as the adjacent eastern islands. However, can`t rule out a few
showers developing over the southern locations of Puerto Rico. A
drier air mass in the mid to upper-levels of the atmosphere will
limit the development of widespread shower activity; the drier air
shows up in the recent TJSJ Skew-T sounding. Also, a frontal
boundary will continue to move near the area during the day. The
front is being supported by a strong upper-level jet and jet streaks
with winds of 90 to 115 kts. The GFS shows a pre-frontal boundary
arriving over Puerto Rico outer waters late Wednesday night into
Thursday morning. The GFS has been consistent in showing the bulk of
moisture moving in from the southwest at 850 to 700 mb; the 850 to
700 mb relative humidity chart displays this. A settle change from
yesterday is the 500 mb temperatures are slightly warmer with
temperatures around -6 to -7 degrees Celsius; however, TJSJ Skew-T
sounding has cape ranging from 1100 to 1200 J/Kg from 22/18Z to
22/21Z. Also, convergence at the surface coupled with increasing
moisture, upper-level instability provided by the upper-level jet,
and diffluence aloft could lead to the development of isolated
thunderstorms over the Atlantic waters tonight. This activity is
prog to move into the northern areas of Puerto Rico Thursday
morning. Then spreading across the southern portions of Puerto Rico
and adjacent Islands during the afternoon on Thursday. However,
high clouds could inhibit or delay thunderstorm development later
tonight and Thursday.

Thursday, the WRF-high resolution model moves the pre-frontal
boundary over the northwestern areas of Puerto late in the
afternoon. Ahead of the boundary expect scattered to numerous
showers that could produce moderate to heavy rainfall. Therefore,
expect ponding of water on roadways and flooding in flood-prone
areas. The front is prog to lose its upper-level support as the
upper- level jet weaken Thursday evening. Due to the warming of 500
mb temperatures and decreasing cape values.

Friday, the frontal boundary is forecast to lose its characteristic
and stall over the area while decaying. This should keep the region
in a marginally moist low level environment, which will be conducive
for isolated to scattered shower development.


.LONG TERM...Saturday through Wednesday of next week...

By Saturday and through the weekend, model guidance suggest
lingering low level moisture but overall improving and stable
conditions aloft with a much drier airmass expected to move
across the region. Expect less frequent early morning passing
showers activity across the islands and coastal waters. This will
be followed by isolated to scattered showers of short duration
during the afternoon hours. Improving conditions are forecast by
Monday and through Wednesday, as the surface high pressure will
once again build and spread eastward across the west Atlantic,
resulting in a more east northeast wind flow on Monday, then
becoming fairly light and more southeasterly by Tuesday.

AVIATION...Mainly VFR conditions expected across all terminals
during the next 24 hours. However, SHRA over NW Puerto Rico may
cause tempo MVFR conditions at TJBQ/TJMZ. ESE winds will continue at
10-15 knots.

MARINE...Although the northerly swell and winds continue to
subside, hazardous marine conditions will continue through this
evening. Thus, Small Craft Advisories continue in effect for most
waters except for coastal waters of western and southern Puerto
Rico, as well as the Mona Passage. Thereafter, small craft
operators are urged to exercise caution due to seas up to 6 feet.
Relatively tranquil marine condition will persist through at least
late Thursday night, when the arrival of another northerly swell
will generate hazardous seas. There is a high risk of rip currents
for beaches along the north coast of Puerto Rico, including
Vieques and Culebra, as well as Saint Thomas and Saint Croix. The
high risk will drop to moderate later tonight.


&&

.AVIATION...VFR conditions are expected to prevail over the next 12
hours across all terminal sites. VCSH/SHRA are possible across
eastern PR and US VI terminals from 22/06 to 22/16Z. Winds are ESE
at 10 to 15 kts.


&&

.MARINE...Seas continued to subside across the regional waters
as the northerly swell continued to fade this morning. There are
no small craft advisories in effect at this time but a slight chop
continues across the Atlantic waters, therefore small craft
operators should exercise caution during the early morning hours.
Improving marine conditions are expected throughout the rest of
the day. Wind will be between 10 -15 kts will occasionally higher
gusts. For the beachgoers, there is a high rip current risk for
the San Juan and Vicinity beaches,the north central beaches of
Puerto Rico and Culebrita beach into the afternoon hours. There is
and a moderate risk of rip currents for most beaches elsewhere
except for the southernmost beaches where there is a low risk.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 73 86 74 / 50 60 60 50
STT 82 76 82 75 / 50 50 50 50

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
503 AM AST Thu Jan 23 2020

.SYNOPSIS...

A more active period of weather is expected as we head towards the
weekend, due to a front that is moving in from the west. Scattered
showers are expected for today and tomorrow, but more persistent
shower activity is possible over the local islands for the
weekend. Though there is only a minimal thunderstorm threat the
next few days, areas where persistent showers set up could give
rise to urban and small stream flooding. Another swell from the
north is expected to arrive tomorrow morning and last most of the
weekend.

&&


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

Several zones of convergence have set up across the area ahead of a
cold front which sweeps southwest from a rapidly deepening low about
150 miles southeast of Bermuda and north of the Leeward Islands. At
5 AM AST, the front was across the Dominican Republic. The
convergence zones were across the western coast of Puerto
Rico and eastern Puerto Rico, but both have weakened
considerably and radar shows only scattered showers in the
Mona Passage and over and south of Cabo Rojo and along the
Cordillera Central. Currently the cold front is progged to enter
Puerto Rico around midday and move through the U.S. Virgin Islands
overnight. Currently lightning is detected with the front but north
of 21 degrees north latitude. Heating over Puerto Rico could enhance
instability enough this afternoon to create isolated thunderstorms
in the area, otherwise only increasing showers over the area is
expected. Satellite imagery also shows tops are relatively warm this
far south. Once the front passes through all the islands and
leaves the area on Friday, winds will be quite weak, but should be
able to return to the east under the influence of a weak high set
to form north of the area behind the front. However by Saturday,
in very weak flow a band of moisture begins to form just tens of
miles north of the islands such that clouds showers are able to
linger over the area the entire period and beyond.

Low pressure at mid and upper levels in the western Atlantic east of
Georgia and north of Puerto Rico will move northeast and will allow
a ridge to build over the area today and move over the Leeward
Islands by Saturday night. This will keep mid levels dry above 600
mb for the entire period. Lower levels however show good vertical
velocity towers in the time-height profile today through at least
Saturday that promises lots of showers generally less than 15 kft
deep forming across the area.


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

The aforementioned front as described in the short term discussion
will still be with us for Sunday, driving additional shower
activity. Upper level atmospheric conditions don`t appear to be
favorable for thunderstorms, with a ridge forecasted to build to
our west in the 250mb GFS model, and a 500mb temperature of only
-5 to -6 for Sunday afternoon. However, this does not mean the
showers won`t be impactful. With the tail of this front expected
to be right over the top of us for the weekend and even lingering
into Monday, areas that receive the more persistent showers could
have periods of urban and small stream flooding. Low level winds
during Sunday and into the workweek are mostly are forecasted to
stay at or below 10 knots, causing slow-moving showers and a
higher chance for flooding.

Models somewhat diverge after the weekend. The European model has us
continuing to be under the front into Wednesday, while the GFS
puts the front a bit to our north, with only bits of moisture
moving in. Regardless, the situation appears a bit drier than this
weekend, and that trend is expected to continue for the remainder
of the workweek.

&&


.AVIATION...

Mainly VFR conds are expected to prevail across all
terminals. However, SHRA over PR could cause tempo MVFR
conds at TJPS/TJMZ and aft 23/14Z ovr TJBQ and aft 23/18Z briefly
at TJSJ. Mtn obscurations are expected thru the pd. Sfc winds
will be vrb as a cold front moves thru the area and sea breezes
interact with the atypical flow pattern. Winds should
switch to northerly in PR from west to east btwn 23/21-24/04Z but
may not switch in the USVI, but remain more SW. Winds will be less
than 10 kt except for some gusts near showers. Max winds west 75-
85kt btwn between FL390-450.

&&


.MARINE...

Calm seas will prevail into tomorrow. However, low pressure to our
north will induce a northerly swell that will arrive tomorrow
morning and be with us till Sunday. It appears that this swell
will not be as long or intense as the last one. However,
dangerous marine conditions are likely, particularly for the
Atlantic waters and local passages. Shower activity will pick up
over the next several days as a front approaches from the west.
The weekend looks particularly active, though conditions will not
be very conducive for thunderstorms.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 82 73 / 80 60 60 60
STT 84 73 83 71 / 30 50 50 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
459 AM AST Fri Jan 24 2020

.SYNOPSIS...

More rainfall is expected today and for the next few days as a
cold front stalls over the region. The thunderstorm threat remains
low, but once again persistent showers could lead to urban and
small stream flooding. More showers are expected to continue
through much of the next week. Another swell will be impacting us
beginning this morning, and lasting through the weekend. Calmer
seas will prevail thereafter for the rest of the workweek.


&&

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

The cold front was just southeast of Saint Croix at 5 AM AST this
morning. Showers persist along the local coastal Atlantic waters and
are generally moving east northeast to east southeast owing to the
shallow depth of the cold air behind the front. Showers are also
moving southeast over the Caribbean southwest of Saint Croix. Modest
moisture will persist just behind the front and the best resolution
models show winds from the south in southern Puerto Rico and from
the north in northern Puerto Rico. This should generate considerable
shower activity in the interior of Puerto Rico by midday or early
afternoon. Forecast soundings show capping is expected just above 10
kft that will limit activity and prevent thunderstorms, but some
showers could produce locally heavy rain and urban and small stream
flooding. The front is now moving only very slowly and may not
completely exit the forecast area today. An upper level ridge will
move through this evening and a jet will continue over the area
through the rest of the weekend.

The GFS is not as bullish on low level omega in the 24/00Z run as it
was 12 hours ago, but expect that showers activity over interior and
northeast Puerto Rico will be healthy and some shower activity will
continue over and around the U.S. Virgin Islands. Showers will not
be as heavy as yesterday. The moisture around the frontal boundary
will continue over Puerto Rico and the U.S. Virgin Islands on
Saturday and low level winds will be quite light and likely less
than 10 knots. According to the GFS, winds at 850 mb do not really
shift from southwest to northwest until late Saturday. Owing to the
confused nature of the pattern around the area, with the decaying
front and the col between the front and the shearline in the
vicinity, the GFS is not consistent with the amount of moisture that
will be available Saturday or Sunday, but has moisture increasing
Saturday into Saturday night that should allow showers to be likely--
at least in the interior, both Saturday and Sunday.


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

Our pesky front will continue to impact us as we begin the workweek.
Though the main low pressure system associated with the front
will be well off to the east, leftover moisture along with
additional moisture being drawn up from the south will keep us
wet. Upper level atmospheric conditions still look uninspiring in
forecast models, so only a minimal thunderstorm threat is
expected. However, given the moist conditions expected over the
weekend and associated saturated soils, additional rainfall on
Monday could lead to urban and small stream flooding. Less of a
flooding threat is expected for Tuesday, though there will still
be some lingering moisture to produce scattered showers. During
this period of the first part of the week, it should be mentioned
that the southern coast where the earthquakes have occurred will
be particularly susceptible to rainfall under these conditions.

For the rest of the week, another cold front moving in from the
west will bring more rainfall across the region. At this point,
Wednesday and Thursday will only see scattered showers. However,
as the front nears on Friday and Saturday, shower activity could
become more numerous according to long range models. Again, upper
level conditions still do not look favorable for thunderstorms,
though an isolated thunderstorm cannot be ruled out.

&&


.AVIATION...

VFR conditions will prevail at TAF sites thru 25/02Z
except for brief MVFR CIGs and psbly VSBYs in SHRA due to cold front
in the vcnty. Aft 24/16Z mtn obscurations in clds and SHRA. Sfc
winds northerly in nrn PR/USVI, southerly in srn PR and TISX. Winds
shift to northerly in TNCM aft 24/15Z, VRB in TKPK. Max winds west
65-80 kt btwn FL340-470 strongest near FL400.

&&


.MARINE...

Another swell is moving in this morning, induced by an area of low
pressure to our north-northwest. This swell does not look as intense
as the last swell, and will not last as long. However, dangerous
marine conditions will continue through Sunday, after which calmer
seas will prevail. Active weather will continue into next week, with
scattered to numerous showers across the local waters.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 74 83 74 / 70 70 60 60
STT 84 73 83 72 / 50 50 70 70

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
506 AM AST Sat Jan 25 2020

.SYNOPSIS...

After a fairly wet past few days, more rainfall is expected
through this weekend and into next week. We will mostly be dealing
with light to moderate shower activity, but the concern is where
persistent showers over a given area result in localized
flooding. By the middle of next week, a drying trend is expected.
Seas will continue to be hazardous into tomorrow, after which
calmer conditions will prevail for the rest of the week.

&&


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

The cold front continues just southeast of Saint Croix and is itself
the focus of showers along its length as well a wider band of
moisture stretching from Colombia northeast to the Leeward Islands
and beyond. Those showers brought generous amounts of rain to Puerto
Rico but only minor amounts to the U.S. Virgin Islands. At upper
levels the ridge moves over the Lesser Antilles and a jet over
western Cuba will sink southeast over the local area today. A short
wave trough will move through the area Sunday morning at upper
levels. A patch of moisture at 700 mb moving across Tobago and the
northern coast of Venezuela will move north and into Puerto Rico and
the U.S. Virgin Islands on Sunday in the northwest half of a high
pressure developing over the eastern Caribbean Saturday. This will
allow another round of showers to form on Sunday. A lobe of that
moisture is also expected to cross over eastern Puerto Rico and the
U.S. Virgin Islands on Monday.

The front will continue a little farther to the southeast today, but
its shearline will return Sunday and Monday to enhance the shallow
showers and cloudiness that will form each day mainly over eastern
Puerto Rico and the U.S. Virgin Islands. Winds ahead of the front
are southeast but winds behind the front and shearline are
northerly. This is creating a pattern of very light winds that will
be dominated by land and sea breeze circulations. GFS and other hi
res models are not in agreement as to the placement of showers, over
Puerto Rico or the U.S. Virgin Islands, although they seem to show
continued showers along the shearline as it pushes southeast and
then returns over the weekend. With winds light and very similar to
yesterday have tried to keep the rainfall pattern similar to that of
yesterday. Amounts should be less in most areas, but local urban and
small stream flooding will be possible again as soils are saturated
and run-off will be slow to seep in. Temperatures will continue
close to seasonal normals.


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

After a fairly wet period over the weekend and to start the
workweek, our weather conditions will very slowly calm down during
the rest of the week. Tuesday through Thursday still look fairly
wet, with more low to mid level southwesterly flow that will bring
in additional moisture. Thus, scattered showers are again likely,
with more light winds leading to slow moving showers during this
period. There is just a minimal thunderstorm threat, but the
potential will again be there for localized areas of flooding
where the most persistent showers set up. Areas affected by
recent earthquakes will still be susceptible to these forecasted
showers. Friday looks to be a transition day, as the flow at low
to mid levels will switch to northerly as a front passes to our
north. Drier conditions are forecasted to prevail behind the
front, and this is suggested by both the American and European
models which adds to our confidence in this forecast.

&&


.AVIATION...

Areas of overcast clouds over Puerto Rico will persist
but overcast is expected to be FL060 and greater. Areas of RA to
continue over local waters and -RA lcly inland. SHRA/RA to dvlp aft
25/16Z ovr PR and arnd the USVI and cont byd 26/03Z with lcly MVFR
conds and mtn obscurations. Sfc winds vrbl less than 10 kt. Maximum
winds WNW 60-75 kt btwn FL 330-470.

&&


.MARINE...

A northerly swell continues to impact the region with wave heights
generally around 5 to 8 feet across the local waters. The swell
will last into tomorrow, after which seas are expected to stay
fairly calm for the rest of the week. However, the weather will
not be calm, as scattered to widespread shower activity is likely
for the next several days.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 72 83 73 / 70 70 30 30
STT 83 72 83 72 / 30 30 20 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
507 AM AST Sun Jan 26 2020

.SYNOPSIS...

Active weather is expected to continue today, as the remains of an
old front continue to persist over the region. Scattered to
numerous showers could lead to localized flooding again for some
areas, particularly given the slow nature of these showers and the
already saturated soils. However, for the latter half of next
week, a drying trend is expected. Seas are calming down as a
northerly swell continues to weaken.

&&


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

Moisture in the lower layers has been carried up into Puerto Rico
and the U.S. Virgin Islands around a high pressure located in the
southeast Caribbean Sea. This is joining moisture already in place
along an old frontal boundary that is now roughly in the vicinity of
Saint Kitts and northeast. This high pressure circulation will keep
relatively good moisture in the lower levels through Tuesday. With
flow in the lower levels very light or southerly, showers will form
in much the same pattern as they have been over the past few days.
Models are showing good chances of rain over the interior of Puerto
Rico and around the U.S. Virgin Islands today. These areas develop
during the day and then decay into steady rains over much of the
area--mainly Puerto Rico during the overnight period, then drifting
north and dissipating. Bands of better relative humidity are seen
forming south of the area and repeating the pattern on Monday. This
has favored showers forming in the interior but then spreading onto
the coastal areas later in the day and during the evening hours.
Slow movements have allowed some favored areas to receive up to 2
inches of rain and a similar pattern is expected through Tuesday.

Upper levels have tended to enhance the action along the old
frontal boundary that is oscillating across the area. A weak upper
level trough moving mainly north of the area toward the east will
move across this morning. Then a broad and weak ridge extending out
of high pressure on the northern border of Brazil will move across
on Monday morning. The strong jet will re-strengthen on Tuesday
marking the area where the upper level long wave trough will move
through the western Atlantic and strengthen he gradient between
itself and the high over South America.


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

Though there are some long-range model differences, the long-
term forecast generally looks drier than the short-term period.
For the middle of this week, the GFS model still has plenty of
moisture in the region from leftover fronts, but only minimal
amounts are forecasted to be over the local islands for Wednesday
and Thursday. However, the European model at this point is
forecasting more moisture and a higher likelihood of scattered
showers under southwesterly flow. Any shower activity is not
expected to be very intense, and there is only a minimal
thunderstorm threat. However, under the more persistent showers,
there will be a threat for localized flooding. Furthermore, low-
level steering winds still look very light, meaning slow moving
showers that increase flooding concerns.

Interestingly, there is actually more model agreement heading
towards the next weekend. Beginning on Friday, a large mid to upper
level ridge is expected to move over and help to dry us out. As
usual, there will still be some low-level moisture around to keep
isolated showers in the forecast. Wind flow is forecasted to be
from the southeast, which will favor showers for the southern and
eastern coasts of Puerto Rico, though these showers will not be
very impactful.


&&

.AVIATION...

Areas of overcast clouds over Puerto Rico will persist
but overcast is expected to be FL045-060 and greater with only
scattered layers below. Areas of SHRA to continue over local waters
but -RA lcly inland should cont to diminish. SHRA/RA to dvlp aft
25/18Z ovr PR and arnd the USVI and cont byd 26/03Z with lcly MVFR
conds and mtn obscurations. Sfc winds vrbl less than 10 kt bcmg
predominantly sea breezes 6-12 kt aft 26/15Z. Maximum winds WNW-NW
55-75 kt btwn FL 220-480 strongest winds at FL310.


&&

.MARINE...

A northerly swell is continuing to weaken this morning, and seas
have gone below Small Craft Advisory criteria. However, small
craft operators should still exercise caution today. Thereafter,
seas are expected to be fairly calm for the remainder of the week.
Ample shower activity is expected across the local waters for
today and the beginning of the workweek.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 83 73 84 73 / 80 60 80 60
STT 83 73 82 73 / 40 40 60 70

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
518 AM AST Mon Jan 27 2020

.SYNOPSIS...

Enhanced moisture continues to linger across the area today. As
such, the potential for shower activity remains high, and will
stay high as we push into midweek. Winds also remain relatively
light, veering from east-southeast today to become more southerly
tomorrow. Because of the weak steering flow, showers will likely
be slow-moving, and there is the risk of localized flooding where
this occurs.

&&

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

Normal to above normal precipitable water(PWAT) content will
continue over the region through the short term period. The GFS
forecast soundings are indicating PWAT peaking at 1.90 inches
today over SJU, and between 1.60-1.70 inches on Tuesday and
Wednesday. This is due to low level moisture from a weak surface
trough over the Caribbean waters being pulled over the forecast
area from a weak high east of the Leeward Islands and the remnants
of an old frontal boundary to the north of the high. This weather
pattern is causing a light southwest steering wind flow, which is
forecast to continue through the short term period. At upper
levels, the jet strengthens on Tuesday as an upper level trough
moves over the western Atlantic. Therefore, any diurnally induced
afternoon shower activity will develop over the interior and drift
over the north central and eastern sections of Puerto Rico each
day, with showers lingering through the early evening hours over
the northeastern sections and across Culebra and Vieques. Urban
and small stream flooding can be expected with this activity.
Models are indicating that the bulk of PWAT is forecast to linger
over the USVI and eastern waters of the islands for the next few
days. For this reason, scattered to numerous showers are forecast
across the USVI through at least Tuesday. By Wednesday, drier air
filters aloft as a mid level ridge builds south of the area.

.LONG TERM...Thursday through Tuesday...

On Thursday, a trend towards gradually decreasing moisture levels is
anticipated to continue across the area. A weak low pressure
system is expected to pass by the area well to our north and help
to sweep away a portion of the remaining moisture lingering over
the area from the most recent frontal boundary remnant. The low to
our north will promote southerly winds across the local islands,
becoming southwesterly late. Meanwhile, a ridge of high pressure
will push off the east coast of the United States and build into
the central Atlantic. Because of this, winds will continue to veer
over the area, with a northerly component Friday into Saturday,
followed by the more-typical easterly flow by late in the day on
Saturday, or possibly southeastern even. There will remain
sufficient moisture, which will generally be confined to the lower
levels, to aid in the development of passing showers during the
overnight hours, especially in the windward portions of the local
islands for the second half of the week. Conditions aloft are
expected to remain stable during this time, aided by ridges at
mid- and upper-levels, contributing to the capping of moisture and
inhibiting significant development. Afternoon showers are still
likely; the location of peak activity is likely to be in the north
on Thursday, the south on Friday, and the west on Saturday.

By late in the day on Saturday, a low will push off the southeastern
US. The timing of this system remains somewhat uncertain, with the
ECMWF showing a slightly earlier approach than the GFS, which has
slowed down some with the 0Z run compared to yesterday`s 18Z run.
Associated with this, winds will veer again to become more
southerly, likely by Saturday night or early Sunday morning.
Moisture is expected to gradually increase as we move into the early
part of the next workweek, and therefore shower activity will also
increase somewhat. Lacking consistency, there remains a slightly
higher than usual level of uncertainty with respect to how much
shower activity is anticipated, in addition to the uncertainty with
respect to the timing. Currently the forecast reflects a compromise
that leans toward the slightly more quickly progressing solution.
This would bring enhanced shower activity to the north of the island
during the afternoon on Monday due to local effects. By Tuesday, a
ridge will push into the Atlantic to our north, and winds will again
become easterly.

&&

.AVIATION...

Mainly VFR conditions expected through at least 16z across all
terminals. SHRA expected to develop in and around TJSJ/TIST/TISX
btw 16z-23z, this could cause tempo MVFR to brief IFR conditions.
Low level winds will continue light with a southerly component,
with exception of a northerly sea breeze developing aft 14z over
the north coast of PR.

&&

.MARINE...

Seas have subsided and are generally less than 4 feet across the
local waters. Though a weak northeasterly swell is expected to
arrive later today, wave heights below 5 feet are expected to
persist into the weekend. For the beachgoers, low to moderate risk
of rip currents persists across the local beaches, with the
moderate risk generally only at north-facing beaches.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 82 73 84 74 / 70 60 70 30
STT 82 73 82 74 / 60 70 70 60

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
421 AM AST Tue Jan 28 2020

.SYNOPSIS...

Enhanced moisture remains in the area, lingering over the Virgin
Islands and eastern Puerto Rico this morning. Decreasing moisture
is anticipated, but sufficient moisture remains in place to
promote the development of afternoon showers. With the steering
flow generally out of the south/southwest today, the peak shower
activity will be in northeastern and interior Puerto Rico, where
localized urban and small stream flooding will be a concern. The
trend towards gradually improved weather will continue into
midweek.

&&

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

A weak surface trough will continue to pool moisture over the USVI
and the eastern sections of Puerto Rico through the short term
period. Southerly steering winds will gradually diminish through
Thursday as the trough pulls away from the region. However, as
moisture lingers over the region and a weak south/southwesterly
steering flow prevails, diurnally induced afternoon showers are
expected each day over the interior and northeastern sections of
Puerto Rico. Localized urban and small stream flooding due to
saturated soils across these areas will be the main threat. Normal
to above normal daytime temperatures are expected across the lower
elevations.

For the rest of PR, sunny to partly cloudy skies are expected over
the west coast with minimum rainfall activity. However, as steering
winds turn more from the south/southeast by late Wednesday showers
are forecast to stream over the southern coastal areas of the island
through the evening hours. Across the USVI, cloudiness and shower
activity will persist through at least Wednesday, with a gradual
improvement on the weather conditions by Thursday as a mid-level
ridge builds across the eastern Caribbean.

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

On Friday, an old frontal boundary will approach the area from the
northwest. This will bring additional moisture into the region, then
help to sweep out the lingering moisture from the preceding system
as we move into the weekend. Increased instability will also be
associated with this system on Friday, though its extent will be
somewhat limited, with a strong ridge in the mid-levels extending
across the Caribbean. A ridge will push into the central Atlantic
off the coast of the US Mid-Atlantic. Under the influence of the
boundary, as well as the ridge to the northeast, winds will
generally have a significant northerly component on Friday, while
the surface ridge moving to north of the area will promote
easterly winds for Saturday. Gradual drying is anticipated
Saturday, with some moisture lingering in the low-levels through
the weekend. Sufficient moisture will remain in the area to
promote the development of passing showers during the overnight
and morning hours, as well as some afternoon showers due to local
effects and diurnal heating.

On Sunday, we once again come under the influence of a frontal
boundary, this time associated with a Nor`Easter well to our north.
With the trough forcing the retreat of the central Atlantic surface
high, wind direction becomes less uniform across the area, and winds
will likely be somewhat variable as we enter the workweek. As the
system presses into the area on Monday into Tuesday, increasing
moisture is expected, as well as some instability. Again, the strong
mid-level ridge will likely inhibit the increase in instability
aloft. With these conditions, increased shower activity and rainfall
amounts are anticipated. A surface ridge will build into the central
Atlantic, and will help bring a return of easterly winds on Tuesday.
Moisture will remain over the area Tuesday and Wednesday, with the
boundary stretched essentially zonally south of the ridge. The low
is expected to be squeezed between two relatively strong ridges,
slowing progression eastward, allowing the pattern to stagnate
somewhat into midweek. Generally, the expectation is for a few
consecutive days of widespread shower activity early next week, much
like we saw at the end of last week. That being said, it would not
take a significant change in the forecast with any of the three
interacting airmasses early next week to cause a substantial
alteration in the forecast here, and changes are likely between now
and then. Currently, the most likely alternative is towards less
rain, either from less moisture associated with the frontal boundary
entering our region or from less time spent stretched across the
local islands (though, of course, the option for more rain cannot
be disregarded).

&&

.AVIATION...

Mainly VFR conditions expected across all terminals through the
forecast period. However, -SHRA in and around the USVI/Leeward
terminals may cause tempo MVFR cigs. Also, between 16z- 23z SHRA
over northeastern PR could affect TJSJ with tempo MVFR conditions.
SCT/BKN lyrs btw FL030-FL120 will continue over the USVI/Leeward
terminals through much of the fcst period. Light winds with a
southerly component will prevail, with sea breeze variations aft
14z at TJSJ/TJBQ.

&&

.MARINE...

Seas continue to be relatively tranquil, with heights less than 5
feet anticipated for the next several days across the regional
waters. There is a moderate risk of rip currents at north-facing
beaches, with generally low risk elsewhere.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 74 85 74 / 60 30 60 50
STT 82 73 84 72 / 60 60 60 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
514 AM AST Wed Jan 29 2020

.SYNOPSIS...

The trend towards gradual drying continues today and tomorrow.
Patches of moisture will continue to slowly stream into the area,
in the generally southerly/southwesterly flow however, which will
help to maintain the pattern of passing showers overnight and in
the morning, followed by afternoon showers, especially in
northeastern and interior Puerto Rico. The weak remnants of an old
frontal boundary will push into the area for Friday, bringing
increased moisture, while winds shift to out of the northeast,
associated with a ridge to our north.

&&

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

A mid level ridge building over the eastern Caribbean will promote a
drier air mass over the region for the next few days. Forecast
soundings are indicating between 1.20-1.50 inches of precipitable
water content through the short term period. Light and variable
winds are expected to continue today and a weak southwesterly
steering wind flow will carry any diurnally induced showers over the
north central and northeastern sections of PR this afternoon. A
similar weather pattern is expected on Thursday, with steering winds
turning more from the south/southeast but without any significant
increase in wind speed. By Friday, northeast trades are expected to
return due to a surface high pressure moving off the Mid-Atlantic
coast of USA. Shallow low-level moisture associated with the
remnants of an old frontal boundary are forecast to move from the
Atlantic waters and enhance diurnal shower activity over the
interior and southwestern sections of PR during the afternoon.
Mostly fair weather conditions are expected across the USVI today
and Thursday, with passing trade wind showers returning on
Friday.

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

Conditions will continue to gradually become drier during the day on
Saturday. Winds out of the east will veer to out of the southeast,
as a surface ridge to our north progresses eastward. Sufficient
moisture is expected to remain across the area in the lower levels
to support some passing showers and afternoon shower activity.

On Sunday, winds are forecast to shift to be more southerly as the
surface ridge continues to pull away, stretching to west of the
local islands, and a frontal boundary begins to approach from the
northwest. This boundary is expected to reach the area by Monday,
with the bulk of the moisture arriving later in the day; enhanced
moisture and instability are expected, though the instability will
be inhibited by a ridge aloft. The model guidance continues to waver
on its solution with respect to the development and progression of
this system. The most recent run of the GFS has the boundary quickly
weakening, and keeps the highest amounts of moisture to the north of
the islands. Either way, increased shower activity, as well as
passing showers are expected as we make our way into the workweek.
Winds are anticipated to shift from generally out of the south to
generally out of the north Monday. The expectation beyond Monday
remains generally the same, with the boundary stretching zonally
across the area by Tuesday, lasting through midweek. Winds are
forecast to shift to be generally out of the east. During this time,
shower activity is likely, with passing showers overnight and
afternoon showers due to local effects and diurnal heating.
Conditions aloft will continue to inhibit any increases in
instability, so convective development beyond just showers is
unlikely. The structure of the boundary and the moist airmass
associated with it become less defined by Thursday. Enhanced
moisture, and therefore showers, will continue over the area, though.

&&

.AVIATION...

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, diurnally induced afternoon
showers over the interior and northern sections of PR could cause
brief MVFR conds at TJSJ. Variable winds expected to continue
through the day, with sea breeze variations after 14z.

&&

.MARINE...

Seas of 5 feet or less are still expected to persist through the
weekend. At the local beaches, there is a moderate risk of rip
currents at north-facing beaches, with low risk elsewhere.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 74 85 74 / 60 50 50 50
STT 83 73 84 72 / 50 50 40 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
511 AM AST Thu Jan 30 2020

.SYNOPSIS...

The drying trend continues today, but there remains sufficient
moisture in the lower levels to aid in the development of
afternoon showers. The area of peak afternoon development will be
in western and interior Puerto Rico for the next few days; the
steering flow today, however, is more southwesterly, which will
lead to showers drifting over northern and northeastern Puerto
Rico late in the day. There is the potential for moderate to
locally heavy rainfall to cause isolated urban and small stream
flooding. The start of next week features another frontal boundary
affecting the area, bringing increased rain.

&&

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

A mid-level ridge will continue to build over the eastern and
northeastern Caribbean through the short term period. This will
continue to promote drier air aloft and strengthen the trade wind
cap across the region. However, the limited available low level
moisture will be enough to aid in the development of diurnally
induced afternoon showers over the interior and western sections of
PR each day. Southeast trades will increase somewhat today but
overall light steering winds with a southwest component will
dominate the flow this afternoon, and any shower that develops over
the interior will drift slowly to the north and northeast through
the evening hours. A surface high pressure moving from the western
Atlantic into the central Atlantic will turn winds more from the
east to northeast on Friday and Saturday. This will favor afternoon
convection over the interior and west/southwest sections of Puerto
Rico each day. Moderate to locally heavy rainfall could lead to
isolated urban and small stream flooding, especially on Friday
afternoon.

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

Winds become more southerly during the morning into midday on Sunday
as a surface ridge to our north progresses eastward. Increasing
moisture is expected as well. A frontal boundary is also expected to
be approaching the region, arriving Monday. Convergence is expected
at the surface on Monday, and increased moisture will push into the
area, associated with the boundary. Additionally, the mid-level
ridge will weaken somewhat over our area, allowing for greater
vertical extent of this enhanced moisture. This will continue into
Tuesday, as well, and increasing shower activity is anticipated.
With the passage of the boundary on Monday, the southerly flow will
become more variable across the area. And, by Tuesday, the southerly
to variable winds are forecast to shift to out of the northeast.
Because of this, the peak shower activity for the afternoon will
likely be in southwestern and interior Puerto Rico on Tuesday.

On Wednesday, the boundary is expected to weaken somewhat and become
less defined, stretching zonally across the region, as the low with
which it will have once been associated continues to pull away to
the northeast. Meanwhile, a ridge will build across the central
Atlantic, promoting easterly winds. These easterly winds will likely
increase slightly in speed somewhat as we make our way towards the
end of the week, though they are expected to remain less than 20
knots over the local waters. The enhanced moisture will linger over
the area through at least Thursday, though with decreasing vertical
extent. On Friday, patches of moisture will continue be carried into
the area, embedded in the trade winds. This will be more than
sufficient to support passing showers during the overnight and
morning hours over the local waters and windward portions of the
local islands, as well as afternoon showers due to local effects and
diurnal heating.

&&

.AVIATION...

Mainly VFR conditions are expected to prevail through the forecast
period across all terminals. However, SHRA developing this
afternoon over mainland PR could cause tempo MVFR conds at
TJSJ/TJMZ/TJBQ btw 16z-22z. Southeast winds at 5-10 knots expected
with sea breeze variations across northern and western PR after
14z.

&&

.MARINE...

Relatively tranquil seas persist across the local waters, at 5 feet
or less, through the weekend, and wind speeds are expected to
generally stay less than 15 knots as well. There remains a moderate
risk of rip currents at most north-facing beaches across the local
islands, with a low risk elsewhere.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 74 83 74 / 40 30 30 40
STT 83 73 83 74 / 40 50 40 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
539 AM AST Fri Jan 31 2020

.SYNOPSIS...Mid-level ridge over the eastern Caribbean will
continue to promote stable conditions through the weekend.
However, enough low level moisture will remain in place to
enhance afternoon shower development over western PR each day. A
frontal boundary is expected to increase shower activity early
next week.

&&

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

At mid- levels ridge located at the eastern Caribbean of Puerto Rico
will continue to generate in dry air for the morning hours today
across the region. However, in the afternoon hours an increase in
the low-level moisture are expected, this in combination with the
local effects can result in shower activity across the region.
This showers will depend directly of the steering wind flow
changing from the northeast by late morning across the region.
Therefore, these shower activity can result in localized urban and
small stream flooding in southwestern and central-south Puerto
Rico this afternoon. This weather pattern is expected at least
until late Friday night to Saturday morning, when a considerable
dry air mass move across the region and limited the shower
activity until Sunday.

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

A col area is expected to develop over the region on Monday as a
cold front stalls just north of the region. At upper levels, a
polar trough is forecast to press against the upper ridge over the
central Caribbean. Although drier mid-level air will continue on
Monday, low level moisture associated to the cold front will pool
gradually over the area and aid in the development of diurnally
induced afternoon showers over west/southwest PR. Meanwhile, a
broad surface high pressure building over the western Atlantic
will push the remnants of the front across the region from late
Monday and through Wednesday as the high moves into the central
Atlantic. This will continue to provide enough low level moisture
each day to result in passing showers across the USVI and eastern
sections of PR during the night and early morning hours, followed
by diurnally induced afternoon showers over western Puerto Rico.
As the high anchors over the central Atlantic, a similar weather
pattern will continue through the end of the week with fragmented
clouds and low level moisture enhancing early morning showers
across the USVI and then in the afternoon over western PR.

&&

.AVIATION...Mainly VFR conditions will prevail during the next 24
hours. However, afternoon convection will bring VCSH to TJMZ,
TJBQ and TJPS between 31/15 - 01/02Z. This could result in bring
MVFR conditions with SCT to BKN at FL030-040. Winds will be light
and variable through most of the period, peaking around 10 knots
after 31/10Z with higher gusts.

&&

.MARINE...Tranquil seas will continue across the regional waters
through the weekend. Seas at less than 5 feet and winds between
5-15 knots will prevail until early next week. A moderate risk of
rip currents will continue through the weekend, mainly for the
northern beaches of Puerto Rico.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 74 86 73 / 20 30 30 20
STT 82 74 83 74 / 20 30 30 20