Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
511 AM AST Thu Oct 1 2020

.SYNOPSIS...Considerable moisture trailing a tropical wave and
favorable conditions aloft due to a lingering TUTT will support
another day of active weather today. Although relatively drier air
along with Saharan dust will filter into the region by the end of
the workweek into the weekend, favorable conditions aloft will
support enhanced convection across the local islands and waters.
Thereafter, a moist and unstable environment should dominate the
local weather conditions through midweek next week with the
passage of tropical waves and influence of upper level lows.
Increasing winds will generate choppy to hazardous marine
conditions through the upcoming weekend.


&&

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

Broad surface high pressure centered over the north central Atlantic
will continue to build and sink southwards across the region while
tightening the local pressure gradient through Friday. This will
result in increasing east southeast tradewinds over the forecast
area. Considerable low level moisture trailing a tropical wave which
exited the region on Wednesday will continue to converge and pool
across the region today into early Friday. Recent satellite derived
precipitable water product, and the earlier TJSJ upper air sounding
as well as forecast upper air sounding all agreed on high layered
precipitable content with values between 1.70-2.0 inches overnight
with a gradual decrease expected later today into Friday as a
moderate to high concentration of Saharan dust moves across the
region. In the upper levels,a lingering Tutt will maintain unstable
conditions through the period providing good ventilation and upper
level divergence as well as cooler temperatures aloft.

That said, expect all the ingredients in place for another day of
active weather across the region with good potential for enhancement
of afternoon convection which be aided by daytime heating and local
effects. In addition, with the moderate to strong low level wind
flow afternoon convection is forecast to develop and stream west
northwest across the interior sections of Puerto Rico, resulting in
showers and thunderstorm development with periods of locally heavy
rains. This will lead to urban and small stream flooding with good
potential of mudslides in areas of steep terrain over portions of
Puerto Rico.

By Friday afternoon and through Saturday, decreasing low level
moisture transport is forecast, as the suspended Saharan dust
particulates will linger across the region while the surface high
pressure ridge builds and remain in place across the region.
However, the upper trough and associated developing low will
continue to deepen and sink southwards across the area. This
increasing instability aloft will favor support periods of enhanced
convection over the regional waters and east coastal sections of
during the overnight and early morning hours, followed by afternoon
convection mainly over the interior and northwest sections of Puerto
Rico, as well as in and around parts of the San Juan metro area
where activity will develop over the east interior and stream
northwest producing periods of locally heavy rains.

For the U.S.Virgin Islands early morning passing showers and isolated
thunderstorms will affect the coastal waters, with afternoon shower
development focused mainly on the west-end and down wind of the
islands today and on Friday. Lesser shower activity is expected so
far on Saturday but an isolated thunderstorms or two cannot be ruled
out during the afternoon hours.

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

Model guidance suggests that a generally moist and unstable
weather pattern will dominate the region through most of the long
term forecast period. This will be the result of a set of tropical
waves streaming across the region with moisture content forecast
to peak around 1.8 to 2.0 inches. In addition, favorable
conditions aloft are expected with a pair of upper level lows
digging south over the region through this period, resulting in
model- estimated 500 mbar temperatures around -7 and -9 degrees F.
Slightly drier weather conditions are expected with the entrance
of relatively drier air between Wednesday and Thursday. However,
sufficient lingering moisture along with local and diurnal effects
will still favor the development of showers and thunderstorms
each afternoon. This will be short- lived with another tropical
wave and associated plume of moisture forecast to reach the
northeastern Caribbean by the end of the workweek. Winds are
expected to remain generally from the east around 5-15 knots, but
brief variations in the flow can be expected with the passage of
each tropical wave and potential induced surface trough.


&&

.AVIATION...Prevailing VFR conds is fcst for all terminals.
SHRA/Isold TSRA ovr regional waters and en route btw islands with
VCSH at most terminals til 01/14Z. Prevailing VFR conds is fcst for
all terminals. Brief Mtn top obscr ovr Ern PR with SHRA and low clds
layers. SHRA/Isold TSRA ovr the interior and W PR fm 01/17Z-01/22Z.
SFC Wnds increasing to 15-20 kt with higher gusts after 01/14z.


&&

.MARINE...Hazardous marine conditions with seas up to 8 feet and
winds up to 20 knots are expected across most of the regional
waters beginning around 2 PM AST this afternoon and continuing
through the weekend. As a result, Small Craft Advisories are in
place. In the meantime, small craft operators are urged to
exercise caution until advisories are in effect. Tranquil marine
conditions are expected by the end of the weekend into early next
week. A moderate risk of rip currents are in effect for most of
the local waters.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 79 90 77 / 50 50 40 20
STT 89 82 89 79 / 40 40 40 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
510 AM AST Fri Oct 2 2020

.SYNOPSIS...During the next few days, unsettled weather
conditions are expected due to the passage of a tropical wave
interacting with a mid to upper level trough increasing shower and
thunderstorm activity. Similar weather conditions will prevail
throughout the forecast period. As a result, urban and small
stream flooding will remain possible. Moderate to fresh easterly
winds will gradually decrease during the weekend into early next
week. Hazardous marine conditions will continue today, improving
tonight into the weekend.

&&

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

Surface high pressure centered over the north central Atlantic will
continue to sink southwards across the region while a vigorous
tropical wave and its associated moisture field moves westwards
across the eastern Caribbean today into early Saturday. Mid to upper
level trough (TUTT) will continue to deepen and sink southwards
across the region with a developing cut-off low forecast to
establish just west of the area between the Mona passage and
Hispaniola by early Sunday. A moderate concentration of Saharan
dust will linger across the region through at least Saturday. The
meandering Tutt and associated developing area of low pressure will
maintain unstable conditions aloft through the period providing good
ventilation and upper level divergence along with cooler
temperatures.

For today, suspended saharan dust particulates will linger across
the region, however the presence of the Tutt in combination with
good low level moisture convergence and local and diurnal effects,
will all favor convective development in and around the islands.
Due to the fairly strong steering flow with winds between 20-25 mph,
expect the activity to quickly stream towards the west northwest
across the islands. However, moisture entrainment is possible in
some areas during the afternoon hours in the form of streamers.
Therefore, urban and small stream flooding will remain possible with
the heavy rains as well as ponding of water on roadways and in poor
drainage areas. The local soil remains loose and saturated in many
areas especially across Puerto Rico and therefore mudslides will
also remain possible in areas of steep terrain.

By early Saturday, a slight erosion low level moisture transport is
anticipated as the trade wind gradually decreases and becomes more
easterly. However with the developing upper low and a weakly induced
low level troughiness, expect afternoon convection to be more
explosive, over the west interior and northwest sections of Puerto
Rico, as well as on the west-end and just downwind of the U.S.
Virgin islands. Some of the afternoon convection will lead to urban
small stream flooding and quick rises in water levels along rivers
and small streams due to period of heavy rains.

On Sunday more of the same expected as a cut off low is forecast to
develop and linger just west of the Puerto Rico between Mona passage
an Hispaniola. Therefore a fairly moist and unstable environmental
will persist with the saharan air layer expected to exit the region
by that time. Consequently enhanced early morning passing showers
can be expected to affect the regional waters and parts of the east
and south coastal sections of the islands. This will be followed by
afternoon convection focused mainly over the central interior and
northern half of Puerto Rico as well as in and around parts of the
San Juan metro area. All in all, for the short term period, the
environmental conditions should remain fairly moist and unstable
with the presence of the Tutt and developing area of low pressure,
along with good low level moisture convergence and diurnal effects
over the islands through the weekend.

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

For Monday, the combination of lingering moisture from the passing
tropical wave to the west and diffluence aloft will maintain
favorable conditions for shower and thunderstorm activity in our
forecast area. This pattern changes between Wednesday and
Thursday, with a less favorable environment for deep convection as
relatively drier air moves in with precipitable water values
falling to less than an inch. However, afternoon shower activity
due to diurnal heating and local effects cannot be ruled out.
Light easterly winds during this time period will concentrate the
strongest activity over interior and western sections of Puerto
Rico.

For the end of the workweek, a wetter pattern returns due to another
tropical wave with precipitable water close to 2 inches moving into
our region. Additionally, a deepening mid to upper level cut-off
low moving southward from the central Atlantic into northeastern
Caribbean will interact with the tropical wave maintaining a very
unstable environment. This will increase once again shower and
thunderstorm development with the possibility of urban and small
stream flooding with the strongest activity. For most of the long
term forecast period, light to moderate easterly winds are
generally expected to remain around 10-15 knots, however, flow
will become variable with the passage of the tropical wave at the
end of the workweek.


&&

AVIATION...Prevailing VFR conds is fcst for all terminals.
SHRA/Isold TSRA ovr regional waters and en route btw islands and
over the particularly over the east and southeastern Caribbean as a
tropical wave continues westward across the area. VCSH at most
terminals except for TJBQ til 02/14Z. Brief Mtn top obscr psbl ovr
Ern PR with SHRA and low clds layers. SHRA/Isold TSRA ovr the
interior and W PR fm 02/17Z-02/22Z. Lgt/Vrb SFC wnds increasing to
15-20 kt with higher gusts between 25 to 30 kts psbl along coastal
areas and with passing showers and thunderstorms activity aft 02/14z.


&&

.MARINE...Small Craft Advisories remain in effect due to seas up
to 7 feet for the offshore Atlantic and Caribbean waters, Mona
and Anegada Passages, and coastal waters of southern US Virgin
Islands, Vieques and eastern Puerto Rico. Elsewhere, small craft
operators are urged to exercise caution due to seas up to 6 feet
and/or winds up to 20 knots. Marine conditions are forecast to
gradually improve today and tonight, leaving hazardous conditions
across the Caribbean waters and Anegada passage through at least
Saturday afternoon. The moderate risk of rip currents continues
for most of the local beaches, except for beaches along the west
coast of Puerto Rico.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 76 86 74 / 30 30 50 20
STT 85 81 84 81 / 40 50 50 50

[cycloneye]

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
552 AM AST Sat Oct 3 2020

.SYNOPSIS...
An upper level trough (TUTT) will continue to become amplified as
it digs further southwest from the central Atlantic into the eastern
Caribbean. An upper low will continue to develop and become cutoff
and linger just west of Puerto Rico Sunday into Monday. This
pattern will maintain very unstable conditions aloft well into
early next week. A moist east- southeast trade wind flow will
persist through the weekend... providing with good moisture
convergence across the area as a vigorous tropical wave and an
elongated plume of trailing moisture crosses the eastern Caribbean.
A broad surface high pressure ridge north of the region and the
tropical wave crossing the region will maintain moderate easterly
trade winds but will gradually diminish today through Sunday. A
low concentration of suspended Saharan dust particulates will
continue to diminish today.

&&

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

Wetter and unsettled weather conditions are expected through the
short-term forecast period. At the mid to upper levels, a digging
upper level low (TUTT) will continue to amplify to the southwest
across the central Atlantic into the central Caribbean Sea. In
association with the aforementioned TUTT, a cutoff low located west-
southwest of Puerto Rico will continue to sink south into the
central Caribbean and south of Hispanola today. Then, a second
cutoff low, also associated to the aforementioned TUTT, is
forecast settle between Puerto Rico and Hispanola by Sunday, but
then move westward over the Greater Antilles through early next
week. These features are expected to generate the instability
favorable for deep convection and thunderstorm development, reflected
in cooler 500 millibar temperatures ranging between -5 and -8
degrees Fahrenheit. Somewhat less favorable dynamics are
anticipated for Monday as the TUTT meanders away and the subsident
side of yet another amplifying TUTT gradually moves into the
northeastern Caribbean from the northeast.

At low levels, a surface high pressure located over the north
central Atlantic will maintain an east to southeast wind flow over
the region. Under this flow, deep plume of tropical moisture,
associated to a tropical wave with axis over the central Caribbean
Sea, is expected to envelop the forecast area through early next
week with model-estimated precipitable water vapor above normal over
two inches expected between midday on Saturday and Monday evening.

In summary, favorable environmental conditions for shower and
thunderstorm development are expected. This activity will favor the
local waters into portions of eastern and southern Puerto Rico,
Vieques, Culebra, and all the US Virgin Islands during the overnight
and early morning hours. As the day progresses, local effects and
diurnal heating will aid in the development of deeper and stronger
shower and thunderstorms over land, favoring portions of the
interior and western sections of Puerto Rico each afternoon.
Development is possible downwind from Sierra de Luquillo and the
local islands, into eastern Puerto Rico and portions of the San Juan
metropolitan area. The timing of peak instability from the second
cutoff low and high low-level moisture convergence will favor peak
convective activity on Sunday. Given the expected weather pattern,
there is a threat for urban and small stream flooding, mudslides in
areas of steep terrain, and possible rapid rises along major rivers
and tributaries each day. However, the potential for significant
impacts is higher for Sunday and Monday, when the steering flow is
expected to diminish.

.LONG TERM...Tuesday through Sunday...
By Tuesday, another Tutt low is forecast to sink southwards
across the northeast Caribbean. This should remain just east of
the region thus favoring subsident and stable conditions aloft.
Consequently less frequent shower and thunderstorm activity is
forecast due to erosion of low level moisture. By Wednesday and
for the rest of the workweek, the pattern changes once again as
The Tutt low deepens and retrogresses over the area resulting in
unstable condtions aloft. This combined with additional moisture
ahead of and accompanying a tropical wave forecast to cross the
eastern Caribbean through Thursday will favor active weather
conditions with good potential for enhanced shower and thunderstorm
development across the islands and coastal waters. Urban and small
stream flood potential will increase with the strongest activity.
For most of the period light to moderate easterly winds are
expected to remain around 10-15 mph, however the steering flow
will become light and variable with the passage of the tropical
wave by the end of the workweek and into the weekend. A gradual
improvement in the weather conditions is forecast by Saturday and
Sunday, however afternoon shower development due to daytime heating
and local effects cannot be ruled out. Afternoon convection should
then be focused mainly over portions of the interior and west sections
of Puerto Rico. Lesser activity and mostly fair weather conditions
is so far forecast elsewhere including for the U.S. Virgin Islands
for the weekend, as high pressure will be the dominant weather
feature.

&&

.AVIATION...SHRA and TSRA expected across most terminals during the
next 24 hours. As a result, MVFR conditions are likely with BKN-OVC
ceilings between FL020-040 and reduced visibility. This conditions
are expected at TJSJ, TJPS, USVI and Leeward terminals through the
entire period,and after 03/16Z at TJBQ. Winds will be generally from
the ESE at 5-15 knots through 03/12Z, increasing to 10-20 knots
thereafter. Higher winds and gusty possible near SHRA/TSRA
activity.

&&

.MARINE...Moderate to fresh east to southeast winds of up to 20
knots will result in choppy and hazardous marine conditions
across the offshore Caribbean waters and Mona Passage through
this afternoon with seas of up to 7-8 feet. Therefore, Small
Craft Advisories will continue in effect. Seas of between 3 and 6
feet will prevail elsewhere and small craft operators should
exercise caution. A moderate risk of rip currents is expected
across most of the local beaches except across western Puerto
Rico, where the rip current risk remains low.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 77 86 76 / 60 60 60 50
STT 86 77 87 78 / 60 60 60 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
420 AM AST Sun Oct 4 2020

.SYNOPSIS...The presence of the persistent mid to upper level
trough (Tutt) and associated low now shifting just northwest of
islands will maintain unstable conditions aloft. This along with
the abundant tropical moisture in place across the forecast area,
will maintain favorable conditions for shower and isolated
thunderstorm development in and around the islands today and into
Monday. A gradual improvement in the weather conditions is expected
by Tuesday. However, by mid-week and through at least Friday the
weather condtions are forecast to quickly change and become very
active with high potential for enhanced showers and thunderstorms
across the forecast area due to the interaction of a strong Tutt
low and the passage of a tropical wave.

&&

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

Wetter and unsettled weather conditions are expected to continue
today and Monday, with less favorables environmental conditions
forecast for Tuesday. At low levels, a surface high pressure located
over the north central Atlantic will maintain an east to southeast
wind flow over the region, with winds gradually weakening throughout
the day. Under this general flow, deep plume of tropical moisture is
expected to continue enveloping the forecast area, with model
guidance still suggesting above normal precipitable water vapor
ranging between 1.9 and 2.1 inches through Monday evening.
Thereafter, a decrease trend in moisture content is expected with
model-estimated precipitable water vapor dropping to around 1.20
inches by Tuesday afternoon.

At the mid to upper levels, a digging upper level low (TUTT) will
continue to amplify to the southwest across the central Atlantic
into the central Caribbean Sea. A cutoff low, associated to the
aforementioned TUTT, is forecast to sink southwestward and settle
between Puerto Rico and Hispanola this afternoon. Then, moving
westward over the Greater Antilles and away from the forecast area
through midweek. This feature is expected to generate sufficient
instability to favor deep convective and thunderstorm development,
which reflects in cooler 500 millibar temperatures ranging
between -5 and -8 degrees Fahrenheit. As mentioned before,
somewhat less favorable dynamics are anticipated for Tuesday as
the TUTT meanders away and the subsident side of yet another
amplifying TUTT moves into the northeastern Caribbean and approach
the forecast area from the northeast.

In summary, favorable environmental conditions for shower and
thunderstorm development are expected once again today and on
Monday. This activity will favor the local waters into portions of
eastern and southern Puerto Rico and the US Virgin Islands during
the overnight and early morning hours. As the day progresses, local
effects and diurnal heating will aid in the development of deeper
and stronger shower and thunderstorms over land, favoring portions
of the interior and western sections of Puerto Rico, as well as
eastern Puerto Rico and portions of the San Juan metropolitan area.
The timing of peak instability and high low-level moisture
convergence will favor peak convective activity today. While this
forecast is based on full clearing of the mid-to-upper level cloud
layer that is currently affecting the forecast area, it is possible
that cloudiness could persist resulting in limited convective
development over land. Regardless of convective development, there
is a threat for urban and small stream flooding with the strongest
activity.

.LONG TERM...Wednesday through Monday
By Wednesday and Thursday a strong deep layered cold core low is
forecast to retrogress and move across the islands in tandem with
a tropical wave. If this unfolds,these features will maintain a
very moist and unstable environment across the forecast area with
high potential for active and unsettled weather conditions at
least through the end of the workweek. Urban and small stream
flood potential will increase with the strongest activity. For
most of the period light to moderate easterly winds between 10 to
15 mph are so far forecast. The overall steering flow will however
become light and variable with the passage of the tropical and into
the weekend. A gradual improvement in the weather conditions is
forecast by Saturday and into the early part of the following week
as a mid to upper level ridge builds aloft and low level moisture
erodes. Occasional patches of trade wind moisture and passing
showers can be expected during the overnight and early morning
hours followed by locally and diurnally induced afternoon showers
and isolated thunderstorms each day. Afternoon convection should
then be focused mainly over portions of the interior and west
sections of Puerto Rico. Lesser activity and mostly fair weather
conditions is so far forecast elsewhere including for the U.S.
Virgin Islands through the weekend, as high pressure will be the
dominant weather feature.

&&

.AVIATION...SHRA and TSRA expected across most terminals during the
next 24 hours. As a result, MVFR conditions are likely with SCT-BKN
ceilings between FL020-040 and reduced visibility. This conditions
are expected at TJSJ, TJPS, USVI and Leeward terminals through the
entire period, and after 04/17Z at TJBQ. Also, SCT-BKN ceilings at
FL080-120 expected through at least 04/14Z. Winds will be generally
variable at 5-10 knots through 04/12Z, turning from the
ESE and increasing to 10-15 knots thereafter.

&&

.MARINE...Small craft operators are urged to exercise caution, as
choppy seas up to 6 feet are expected today. Winds will continue
from the east southeast between 10-20 kt with occasionally higher
gusts. Showers and isolated thunderstorm activity is expected over
the regional waters today, with periods of locally heavy rain and
areas of frequent lightning. Moderate risk of rip currents for
many of the local beaches of Puerto Rico and adjacent islands.
There is a moderate risk of rip currents for the east end of St
Croix and a low risk of rip currents for the rest of U.S. Virgin
Islands.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 77 88 77 / 60 60 60 40
STT 87 79 87 77 / 50 50 50 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
426 AM AST Tue Oct 6 2020

.SYNOPSIS...More limited shower activity is expected today due to
drier air moving across. By later tonight into Wednesday, however,
conditions will turn unsettled once again as a vigorous upper-
level low moves across and west of the region. This will result
in an increase in shower and thunderstorm activity. A more stable
weather pattern is expected by the end of the work week as a mid
and upper-level ridge and drier air will limit shower activity.

&&

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

A few showers brushed the northeast and southeast coasts with very
minor accumulations, otherwise good shower activity with a few
isolated lightning strikes occurred over the local Caribbean and
Atlantic waters only with up to 2.5 inches of rain seen south of
Penuelas in the outer Caribbean waters. Low level flow was mostly
east with a slight northerly component.

Drier air from the north northeast has moved across Puerto Rico and
the northern U.S. Virgin Islands, but excellent moisture was still
covering the Caribbean, where showers were most abundant early this
morning.

A vigorous upper level low was north of Guadeloupe at 20 degrees
north latitude and is expected to move west along 19 or 20 north
until it reaches Haiti Wednesday. This represents a considerable
departure from the solution 24 hours ago, so confidence in this path
is only moderate. Nevertheless there is fairly good agreement in the
ECMWF that moisture will return on Tuesday night from the southeast
with a low level trough and will combine with good divergence aloft
over Puerto Rico and the U.S. Virgin Islands tonight to produce
considerable rainfall and unstable weather that will continue into
Wednesday morning. With southeast low level flow, there is concern
that this could result in very heavy rain over the mountains of
southeast Puerto Rico during the morning with significant rainfall
spreading across Puerto Rico later in the day. Again with only
moderate confidence in the model solution the track of the upper
level low will need to be monitored closely.

Although some drying takes place overnight on Wednesday, patches of
moisture will move through on Thursday during the day that will
trigger more showers and isolated thunderstorms.

Hurricane Delta, now south of western Cuba, is expected to continue
northwest and away from the area such that no direct effects will
impact the local forecast area.

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

Fair weather conditions are expected on Friday as moisture content
is expected to drop to below normal levels and mid and upper-
level ridge overhead will result in subsidence aloft. Therefore,
limited shower activity is expected across the area, with western
Puerto Rico possibly observing some afternoon activity due to the
tipical diurnal and local effects. In contrast to previous runs,
model guidance is indicating the upcoming weekend will turn
unsettled as a tropical wave currently located over the central
Tropical Atlantic will move across, resulting an increase in
moisture once again with precipitable water values approaching
2.00 inches. Therefore, the combination of this deeper moisture
along with daytime heating and local effects will result in
enhanced convection across interior and western portions of Puerto
Rico both Saturday and Sunday afternoons with some scattered
shower activity possible across eastern Puerto Rico and the USVI
during the overnight and early morning hours.

Model guidance suggests a continuation of unsettled weather
conditions during the early to middle portion of next week as a
mid and upper-level trough amplifies across the west-central
Atlantic, inducing a broad low-level trough. This broad low-level
trough will maintain moisture levels near to above normal and
also result a very light steering flow with the flow diminishing
to less than 10 knots. Therefore, it appears that enhanced
afternoon convection will be likely, especially across interior
and western Puerto Rico.

&&

.AVIATION...A drier airmass has spread into the fcst area from
the NNE, this will limit convection, but sct SHRA and isold TSRA are
still expected to dvlp over the area. TSRA ovr wrn and interior PR
will produce local MVFR conds and mtn obscurations mainly from 06/17-
22Z. Conds over ern PR will deteriorate considerably aft 07/06Z with
MVFR/IFR conds and mtn obscurations in +SHRA/TSRA ovr ern PR and
extending SE ovr the lcl waters and TISX. Sfc winds east 8-16 kts
with hir gusts aft 06/14Z and sea breeze influences. Maximum winds
NNE 50-90 knots btwn FL310-495, strongest at FL400. Winds will
decrease rapidly during the day with apch of upr lvl low.

&&

.MARINE...More tranquil marine conditions are expected today with
seas expected to remain at and below 5 feet with easterly winds
of up to 15 knots. Tranquil seas are expected to prevail during
the next several days. A moderate risk of rip currents is expected
across the north coast of Puerto Rico, the east coast of Vieques,
and the north and east coast of Culebra and Saint Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 78 88 78 / 30 50 60 30
STT 88 79 87 79 / 40 70 80 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
358 AM AST Thu Oct 8 2020

.SYNOPSIS...Generally good moisture with high pressure aloft and
only weak waves or troughs moving through the area will bring
scattered showers during the overnight and early morning hours for
eastern and southeastern Puerto Rico with afternoon convection of
moderate strength bringing showers and thunderstorms to northwest
and interior Puerto Rico and downstream from El Yunque into the
Greater San Juan and Bayamon Metropolitan area. The U.S. Virgin
Islands will see limited shower activity on most days with better
showers Sunday and Monday.

&&

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

A mid and upper-level ridge is building over the area, resulting in
a more stable atmosphere. Despite this, moisture will continue to
remain near to slightly above normal with precipitable water values
at around 2.00 inches in south to southeast flow. As a result,
this moisture will combine with diurnal heating and sea breeze
convergence to generate afternoon convection across portions of
interior as well as north-central and northwestern Puerto Rico.
Some showers may also develop across portions of the San Juan
metro-area. The steering flow is expected to remain light, under
10 knots, causing slow-moving activity so the potential exists for
some localized urban and small stream flooding to materialize as
well. Across the USVI, only isolated to widely scattered showers
can be expected.

Later tonight and during the day on Friday, a somewhat drier air
mass is expected to move in with the flow becoming northeasterly.
This combined with the ridge aloft prevailing overhead will result
in mostly fair weather conditions across most of the area.
Nevertheless, there will still be sufficient moisture at low-levels
to combine with diurnal heating and local effects to generate some
afternoon convection across the southwestern quadrant of Puerto
Rico.

Moisture, associated with the leading edge of a tropical wave,
increases once again on Saturday. This will result in an increase in
shower activity with some activity expected across portions of
eastern Puerto Rico and the USVI during the morning hours followed
by development across interior and western Puerto Rico during the
afternoon hours. Despite this increase in moisture, the
aformentioned mid to upper-level ridge will continue to have an
influence over the area, limiting the potential for significant
activity to develop.

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

Rich moisture continues across the area Sunday and Monday as a
trough in the area produces favorable conditions for widespread
shower activity. Some urban and small stream flooding is
indicated. High pressure aloft will begin in the Bahamas and
drift slowly west into the Gulf of Mexico Monday and Tuesday. Low
pressure at upper levels well to our northeast will force a short
wave trough into the local area on Wednesday.

At the surface, high pressure digs into the western tropical
Atlantic so that low level flow becomes mostly southeast with some
brief deviations. Patchy moisture Tuesday and Wednesday will then
bring showers and isolated afternoon thunderstorms to northwest
and central Puerto Rico with some possibility for streamers off of
El Yunque to generate showers over San Juan, Bayamon and
surrounding municipalities. Wind flow, being gentle to moderate
will allow some areas to see urban and small stream flooding those
days as well though with moisture more limited, this minor
flooding will not be as prevalent.

&&

.AVIATION...Mainly VFR conditions are expected to prevail across
all terminals. However, SHRA/TSRA are expected to develop across
portions of interior, north-central and northwestern Puerto Rico
between 08/16z and 08/22z, affecting the vicinity of TJBQ/TJMZ
and TJSJ. Winds will continue light and variable through 08/12z,
increasing to up to 10 knots from the SE-SSE with sea breeze
variations after 08/14z.

&&

.MARINE...Winds will continue less than 15 knots through the
period. With no significant storms moving through the Atlantic
swell will also be less than 3 feet. This will bring some of the
lightest seas we have seen all year for such an extended period.
Rip current risk will be low for the U.S. Virgin Islands and
moderate only for Sunday through Monday night for the northern
coast of Puerto Rico.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 90 77 / 40 20 30 40
STT 88 81 88 81 / 30 20 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
440 AM AST Fri Oct 9 2020

.SYNOPSIS...A pattern of weak features under the influence of high
pressure aloft, but generally good moisture will bring daily
showers and thunderstorms to the area with localized urban and
small stream flooding. Instability will increase on Monday and
through the remainder of next week.

&&

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

A mid and upper-level ridge along with a drier air mass will result
in mostly fair weather conditions across most of the local area for
today. Enough low-level moisture will be present to combine with
diurnal and local effects and spark afternoon showers and isolated
thunderstorms across the southwestern quadrant of Puerto Rico as the
steering flow will be from the east-northeast. Areas of localized
urban and small stream flooding may be possible in the most
persistent activity.

Moisture once again increases later tonight into Saturday as a
tropical wave approaches the area. Its axis will cross Puerto
Rico during the afternoon hours. The precipitable water increases
to 2.0-2.2 inches with this wave. Therefore, an increase in
rainfall activity is anticipated. Scattered showers will be
increasing across the local waters later tonight into Saturday
morning, with some of the activity expected to affect portions of
the USVI and eastern Puerto Rico. Then, during the afternoon
hours, as the moisture combines with diurnal and local effects,
more significant shower and thunderstorm activity is expected
across interior and western Puerto Rico with some activity also
possible across the San Juan metro area. Areas of urban and small
stream flooding will be possible with the heaviest and most
persistent activity. The axis of the tropical wave will be pulling
away into Hispaniola by Sunday, however, the associated moisture
will continue to linger across the area and will aid in producing
another round of afternoon convection, mainly across interior and
western portions of Puerto Rico.

.LONG TERM...Monday through Thursday...
Moisture will generally fluctuate between 2 and 1.6 inches during
the period, with low level flow generally oscillating between
east and southeast. A negatively tilted tropical wave that enters
the Caribbean from the east will pass mainly south of the islands
on Monday, but it tends to fragment on Tuesday such that the axis
of the wave as far north as Puerto Rico and the U.S. Virgin
Islands does not arrive until Wednesday. It is briefly
accompanied by fairly decent vertical motion Wednesday. This is
also when the best precipitable water of the period is forecast.
500 mb temperatures tend to fall from Monday through the following
Sunday with the largest drop coming on Monday. This will allow
conditions to become more favorable to convection. It is also
noted that several short wave troughs move through a more
stationary TUTT located over the area from a low pressure to the
northeast Tuesday and Thursday. This will bring sufficient
showers to the area of an intensity sufficient to generate urban
and small stream flooding pretty much each afternoon during the
week.

&&

.AVIATION...Mainly VFR conditions are expected to prevail across
all terminals. SHRA and iso TSRA activity expected across interior
and southwest PR between 09/16z and 09/22z, affecting the vicinity
of TJPS. Winds light and variable through 09/12z, increasing to
between 8 and 12 kts from the ENE with sea breeze variations after
09/14z. Maximum winds NE at 25-30 kt btwn FL350-430.


&&

.MARINE...Marine conditions remain tranquil with storms in the
Atlantic forcing wind driven seas into the tropical Atlantic and
generally missing Puerto Rico and the U.S. Virgin Islands. Seas
will remain similar through Monday and then on Tuesday and
Wednesday should become even more quiet. Small craft advisories
are not expected for the next 7 to 10 days. Rip current risk
remains low except for a moderate risk on the northern beaches of
Puerto Rico Sunday night through Monday night.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 77 89 78 / 30 50 30 40
STT 91 81 89 81 / 20 40 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
456 AM AST Sat Oct 10 2020

.SYNOPSIS...A tropical wave will generate shower and thunderstorm
activity affecting Puerto Rico and the U.S. Virgin Islands through
the weekend. Later, an upper-level ridge will persist on Sunday
and Monday but with sufficient moisture to cause localized shower
and isolated thunderstorms in the afternoon. The upper-level
ridge will gradually erode as an upper-level trough settles into
our area on Monday bringing unstable weather throughout the week.
The unsettled pattern will be enhanced by the arrival of a
tropical wave by the end of the workweek promoting once again
urban and small stream flooding over our area.


&&

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

A tropical wave will continue to cause shower and thunderstorm
activity across the region today. Scattered to locally numerous
showers with isolated thunderstorms were noted during the overnight
hours across portions of northern and eastern PR and as well as
across the USVI. Between 0.50-1.50 inches of rainfall was estimated
with this activity under a persistent northerly wind flow. As the
tropical wave continues to move west and across the islands, winds
are forecast to shift from the east to east southeast and diurnally
induced afternoon showers and thunderstorms will favor portions of
the eastern interior, central and western PR. Urban and small stream
flooding is expected with this activity. Scattered showers with
possible isolated thunderstorms are expected across the U.S. Virgin
Islands.

An upper level ridge that extends from the southwestern Atlantic
into the northeastern Caribbean will gradually erode through the
short term period, as an upper level trough builds to our northeast
by early next week. At lower levels, lingering moisture from the
departing wave on Sunday will combine again with local effects and
day time heating to result in shower and thunderstorm activity over
the same areas as today. A moist southeast steering wind flow will
continue on Monday and once again, showers and isolated
thunderstorms are expected to develop over the eastern mountains
into San Juan and vicinity as well as across the western half of
Puerto Rico.

Southeasterly winds will result in heat indices reaching the low 100
degrees today across portions of the north central to
northeastern sections of Puerto Rico.

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

The upper-level ridge will continue to erode as a short wave
upper-level trough is anticipated to move into the northeast
Caribbean and sets over our region and will remain for the rest of
the forecast period. 500 mb temperatures will decrease maintaining
unsettle conditions during this period. Moisture availability
between Tuesday and Wednesday will be patchy with variable
precipitable water around 1.7 inches. Under this pattern, with
mid- to upper-level instability establishing during the workweek,
moderate amounts of moisture and moderate wind flow, expect
isolated shower activity to develop over the local area. Local and
diurnal effects will generate afternoon convection over interior
and northwestern portions of Puerto Rico including San Juan metro
area between Tuesday and Wednesday and change to the southwestern
portions as winds gradually change to a northeasterly wind flow on
Thursday. Localized urban and small stream flooding are possible
with the heaviest rainfall events. Precipitable water will
continue to increase for the rest of the workweek reaching values
of more than 2 inches as a tropical wave moves across Puerto Rico
and USVI on Friday. This will make conditions much more favorable
for convection and once again the increasing possibility of urban
and small stream flooding.

&&

.AVIATION...Tempo MVFR early in the fcst at TJSJ due to SHRA/iso
TSRA as a tropical wave moves across the forecast area today.
Then, afternoon SHRA/TSRA across mainland PR should continue to
cause brief MVFR conds at times across the PR terminals. At least
VCTS is forecast for most of the terminals today. Low level winds
with a 10- 15 kt wind component prevailing through 16z, shifting
more E-ESE through the afternoon hours.

&&

.MARINE...Mariners can expect winds at 15 knots or less with
tranquil seas across the local and regional waters with seas of up
to 4 feet. Shower and thunderstorm activity is anticipated across
the local and regional waters through the weekend as a tropical
wave moves across our area today.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 79 89 77 / 60 50 40 30
STT 84 81 84 80 / 60 50 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
453 AM AST Mon Oct 12 2020

.SYNOPSIS...For today, shower and thunderstorm activity is expected
during the afternoon hours. As an upper level ridge weakens and
moves westward, an upper level trough builds and moves over our area
by midweek. With an approaching tropical wave as well by the end of
the week, shower and thunderstorm development is possible over a
wide area increasing the potential for urban and small stream
flooding through Saturday. Shower activity between late Saturday and
Sunday will diminish as a mid to upper level ridge settles over our
region. However, shower and thunderstorm development due to local
effects cannot be ruled out in the afternoon hours. For most of the
workweek, tranquil seas are expected. There is a moderate risk of
rip currents for some northern beaches of Puerto Rico and northern
coast of Culebra for today.

&&

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

For today, the combination of the available moisture, daytime
heating and local effects will result in afternoon shower and
thunderstorm development over portions of the interior and western
Puerto Rico. Urban and small stream flooding is expected across
these areas with the heaviest showers. Scattered showers are
expected to develop across San Juan and vicinity and from streamers
developing off the U.S. Virgin Islands. Max temps are forecast to
range from the high 80s to the low 90s across the lower elevations
and heat indices could reach the low 100 degrees across the north
central areas of Puerto Rico.

An upper level trough is forecast to build east-northeast of the
Leeward Islands by midweek, while an upper level ridge over the
southwestern Atlantic weakens and move further west of the area
during the next day or so. 500 mb temps are forecast to decrease
from -5C today to -7C on Wednesday. At lower levels, a moist
southeasterly wind flow and weak perturbation are expected to
increase precipitable water content from around 1.70 inches today to
near 2 inches by Tuesday morning and slightly higher on Wednesday.
This will increase the areal coverage of showers and thunderstorms
each day and the potential for urban and small stream flooding, as
well as localized flash flooding.

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

A short-wave upper-level trough will continue moving southwestward
as low-level southeasterly winds pull moisture ahead of a tropical
wave over the islands increasing precipitable water values of more
than 2 inches on Thursday. As the upper-level trough moves over our
area, temperatures are expected to cool down at 500 mb between -6.5
to -7 degrees C increasing unstable conditions aloft. This will
cause an increase of shower and thunderstorm activity, especially If
the divergent side of the upper-level trough coincides with
afternoon surface heating. These conditions will be compounded by
the arrival of a tropical wave between Thursday and Friday. However,
the strength of the tropical wave may weaken as drier air mass to
the northeast slowly erodes it prior its arrival over the forecast
area. Nevertheless, there is a potential for urban and small
stream flooding with the heaviest rainfall activity for the end
of the workweek. On Saturday, remnant moisture from the tropical
wave could possibly continue aiding in shower development before a
mid- to upper-level ridge settles over our region for the rest of
the forecast period. Model guidance suggests warm and dry air
advection in the mid-levels possibly reducing unstable conditions.
However, shower and thunderstorm development due to local effects
cannot be ruled out in the afternoon hours.

&&

.AVIATION...Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. However, TSRA is expected to
develop over western PR btw 16z-22z, this could cause tempo MVFR
cigs at TJBQ. Low level winds E-ESE at 10-15 kts.


&&

.MARINE...For most of the workweek, tranquil seas are expected with
seas and east-southeasterly winds remaining below 4 feet and 15
knots, respectively. Shower and thunderstorm activity will increase
through the week due to the effects of an upper-level trough and an
approaching tropical wave. There is a moderate risk of rip
currents for the northern beaches of Puerto Rico and northern
coast of Culebra for today.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 90 77 / 20 20 50 40
STT 88 79 88 78 / 30 30 50 60

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
501 AM AST Tue Oct 13 2020

.SYNOPSIS...

Unstable condtions aloft due to an upper level trough in
combination with a moist environment at low levels will aid in
the development of scattered showers and isolated thunderstorms
for the next couple of days. Rainy condition`s will persist and
become more widespread with the arrival of a tropical wave across
the area late Thursday through early Saturday. The weekend
through Monday will slowly transition to more stable condition as
a building mid to upper level ridge settles over our region.
However, shower and thunderstorm development due to local effects
cannot be ruled out in the afternoon hours. Seas will remain below
5 feet during the week with moderate risk of rip currents for
some northern beaches remaining today.

&&

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

An upper level trough east-northeast of the region will increase
instability across the region through the short term period. 500 mb
temps are forecast to cool from -5.5C today to -7.5C on Thursday. At
low levels, a moist east to southeast steering wind flow will
persist and an easterly perturbation embedded on this flow will aid
in the development of scattered showers with isolated thunderstorms
across the regional waters and across portions of the islands
through the day. Day time heating and the sea breeze convergence
will cause thunderstorm development with heavy showers this
afternoon over the interior, north central and western sections of
PR.

Tropical moisture will continue to pool across the forecast area and
steering winds are forecast to decrease from around 10 kts today to
5 kts by Wednesday. This will cause slow-moving showers and increase
the risk of flash flooding and mudslides in areas of steep terrain.
Rainy conditions will continue on Thursday as a tropical wave moves
across the area. This wave and unstable conditions aloft should
increase the areal coverage of showers and thunderstorms across all
the islands.

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

Model guidance continues suggesting wetter conditions on Friday
with the arrival of a tropical wave from the southeast coupled
with an upper-level trough. This tropical wave, located in the
over the eastern Caribbean, has a 30% chance of formation in the
next few days, however, upper- level winds are expected to be less
conducive for tropical cyclone development before it arrives over
Puerto Rico and USVI. There also exist some discrepancies between
the models regarding how vigorous this tropical wave will be when
it reaches our region. Both GFS and ECMWF put the tropical wave
over us by the end of the workweek, generally being eroded by a
drier air mass behind it. However, ECMWF is more aggressive on
this pattern with a weaker upper-level trough than GFS.
Regardless, both models suggest fairly moist environment to
support shower and thunderstorm development over a widespread
area. Urban and small stream flooding as well as ponding of waters
will be possible through early Saturday. As both the tropical
wave moves northwestward and the upper- level trough erodes, a
strong mid to upper level ridge will build from the north Atlantic
and settle over the forecast area between Saturday to Monday.
Over the weekend, precipitable water values will slowly decrease
as ridging occurs aloft, however, residual moisture will still be
present for shower and thunderstorm activity to develop especially
during afternoon hours due to local and diurnal effects. Strong
subsidence effects with the building/expanding mid to upper ridge
will unfold early Monday prompting stable conditions. Still,
sufficient low-level moisture combined with daytime heating could
produce localized showers and thunderstorms during afternoon
hours.

&&

.AVIATION...Mainly VFR conditions are expected to prevail across all
terminals. However, brief MVFR conds are possible through the
morning hours across the USVI terminals due to SHRA. TSRA is
expected to develop over the interior and western PR btw 16z-22z,
this could cause tempo MVFR cigs at TJBQ/TJSJ. Low level winds E-ESE
at 10-15 kts, with sea breeze variations expected aft 14z.


&&

.MARINE...Tranquil marine conditions with seas below 5 feet and light
to moderate winds up to 15 knots are expected across the regional
waters through the end of the workweek. This will maintain
conditions below small craft advisory criteria. Shower and
thunderstorm activity will increase through the week due to the
effects of an upper-level trough and an approaching tropical wave.
There is a moderate risk of rip currents for some northern
beaches of Puerto Rico today.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 88 79 / 50 40 60 50
STT 88 78 88 79 / 50 60 50 60

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
506 AM AST Wed Oct 14 2020

.SYNOPSIS...

Unstable conditions will continue through the end of the workweek,
as an upper level trough to our northeast extends into the local
area and a tropical wave moves across the region on Thursday and
Friday. Urban and small stream flooding is expected as well
as localized flash flooding and mudslides in areas of steep terrain
with the heaviest showers over mainland Puerto Rico. An upper
level ridge will settle across our area over the weekend but
sufficient lingering tropical moisture from the passage of the
tropical wave could possibly generate some shower and
thunderstorm activity. Tranquil marine conditions and light to
moderate winds up to 15 knots are expected across the regional
waters through early Thursday. Later, seas of up to 6 feet through
Friday in some areas over the local waters could be possible due
to the approaching tropical wave. Moderate risk of rip currents is
forecasted for the weekend for northern beaches of Puerto Rico
and local islands.

&&

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

Unstable conditions will continue through the end of the workweek,
as an upper level trough to our northeast extends into the local
area and a tropical wave moves across the region on Thursday and
Friday. This will cause pooling of tropical moisture across the
forecast area, with precipitable water content fluctuating between
2.00-2.25 inches during the next few days. Light steering winds with
an east to southeasterly component are expected today, this will
increase the flooding potential across all the islands due to slow
moving storms. Urban and small stream flooding is expected as well
as localized flash flooding and mudslides in areas of steep terrain
with the heaviest showers over mainland Puerto Rico.

The areal coverage of showers and thunderstorms will increase with
the passage of a tropical wave, currently located east of the
Leeward Islands, between Thursday and Friday as the wave moves
westward across the islands. Winds are expected to increase with the
passage of the wave and thunderstorms should bring squally weather
across portions of the regional waters. Heavy showers over saturated
soils during this period will likely cause flash flooding across
Puerto Rico and the U.S. Virgin Islands. Minor river flooding is
also possible.

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

As the tropical wave continues its path westward by early Saturday,
a remaining tail of moisture will fluctuate across our area through
late Monday. At the same time a building upper level ridge will
settle over the forecast area as a very strong upper level low and
an induced surface trough over the central tropical Atlantic moves
southward and remain to the northeast of Puerto Rico and U.S. Virgin
Islands. A mid level dry airmass will be advected by this strong
upper level/surface low, however, it will remain just north of our
region. Latest model guidance now puts the mid level moisture
boundary to our north with a moister environment than previously
suggested. Precipitable water values will decrease from 2.2 inches
early Saturday to almost 1.7 inches through Monday and 500 mb
temperatures will remain at or below -6 degrees celsius.

Although some subsidence will be present over the weekend through
Monday due to ridging aloft, moderately favorable conditions will
still be present for occasional passing showers in the morning
hours and afternoon shallow convection development with possible
deep convective activity over areas with stronger local surface
heating. Urban and small stream flooding are possible in areas
with the heaviest showers especially over saturated soils.
However, there exist high uncertainty in the forecast depending
where the mid level moisture gradient will remain throughout this
period. According to model guidance, precipitable water values
could increase on Monday and Tuesday to more than 2 inches as the
mid level moisture boundary moves northward increasing the
probability of shower and thunderstorm activity across the area,
but, as mentioned above, high uncertainty exist for the long term
forecast.


&&

.AVIATION...Mainly VFR conditions are expected to prevail across all
terminals early in the fcst period. However, TEMPO MVFR conds are
possible through the rest of morning hours across the USVI terminals
due to +SHRA. Also, TSRA is expected to develop over the eastern
interior, central and western PR btw 16z-22z, this will cause tempo
MVFR conds at TJBQ/TJSJ. Low level winds ESE around 10 kts, with sea
breeze variations aft 14z.


&&

.MARINE...Tranquil marine conditions with seas below 5 feet and light
to moderate winds up to 15 knots are expected across the regional
waters through early Thursday. This will maintain conditions
below small craft advisory criteria. Later, seas of up to 6 feet
trough Friday in some areas over the local waters could be
possible due to an approaching tropical wave. Shower and
thunderstorm activity will persist through the week due to the
effects of an upper-level trough and the approaching tropical
wave. Moderate risk of rip currents is forecasted for the weekend
for northern beaches of Puerto Rico and local islands.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 77 88 78 / 60 50 80 60
STT 88 79 87 78 / 50 50 70 70

[cycloneye]

 https://twitter.com/NWSSanJuan/status/1316436539375747073

[cycloneye]

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
536 AM AST Thu Oct 15 2020

.SYNOPSIS...
An amplifying Tropical Upper Tropospheric Trough (TUTT) will
increase instability across the northeast Caribbean through the
next few days. This upper-level feature will interact with plenty
of tropical moisture associated with a tropical wave today and
Friday. Any prolonged heavy rain could lead to flash flooding and
mudslides due to soil saturation across portions of Puerto Rico.
Therefore, a Flash Flood Watch is in effect for Puerto Rico and
the U.S. Virgin Islands from this afternoon through Friday
evening.

&&

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

An approaching upper level trough will increase instability
through at least Friday. At the surface, a tropical disturbance,
now near the Lesser Antilles, will move over the area later today,
bringing abundant tropical moisture over the area. GOES
satellite-derived products indicated precipitable water vales
above 2 inches. Winds will prevail from the east but are forecast
to shift from the east-southeast as the disturbance moves closer
to the region. That said, shower activity is expected to slowly
increase mainly across the local waters, the U.S. Virgin Islands
and eastern Puerto Rico through the morning hours. Taking into
consideration that soils are already saturated and the likelihood
to observe persistent heavy rainfall today, the potential for
flash flooding is considered high for the islands. This weather
pattern is forecast to persist through at least Friday evening.
Therefore, a Flash Flood Watch is in effect for Puerto Rico and
the U.S. Virgin Islands throught Friday Evening. Also, any period
of prolonged heavy rainfall will result in mudslides in areas of
steep terrain.

Although a ridge is forecast to slowly build from the west into
the region by Saturday, the trailing moisture of the tropical
disturbance interacting with local effects could produce another
round of afternoon convection.

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

A ridge building at mid to upper-level will promote subsidence
aloft and dry air at these levels. Although this feature will
promote unfavorable atmospheric conditions for deep convection
through at least early Monday, occasional passing showers in the
morning hours and afternoon shallow convection are possible over
areas with stronger local surface heating.

A TUTT low across the Central Atlantic and an induced surface low
will move southwestward near the Northeast Caribbean around early
next week, between Monday afternoon and Tuesday. Then, the
surface low will move more westward near the local Atlantic Ocean,
inducing a southerly wind flow across the region. This wind flow
will lift plenty of tropical moisture from the ITCZ over the
islands of Puerto Rico and the U.S. Virgin Islands Tuesday and
Wednesday. Winds are forecast to return from the east as a
surface-high pressure builds across the North Atlantic Ocean by
the second part of next week.

&&

.AVIATION...

VFR conditions are expected thru 15/12Z. Then, a tropical
disturbance moving into the region will bring an increase in
SHRA/TSRA over/near TISX/TIST/TJSJ/TKPK/TNCM, mainly by around
15/15Z and into the evening. Therefore, TEMPO MVRF are likely for
those sites. Calm to light and VRB winds thru 15/13z, becoming
more from the E-ESE at 10-15 knots, with sea breeze variation and
occasional higher gusts.

&&

.MARINE...

Seas will remain relatively tranquil through the morning hours.
However, seas and winds are forecast to increase across the
Anegada Passage and the Atlantic Waters as the tropical wave moves
closer to the islands. Therefore, a small craft advisory is in
effect for the Atlantic Offshore Waters and Anegada Passage. Also,
the potential for showers and thunderstorms will increase this
afternoon into Friday evening due to the aforementioned tropical
wave. Mariners should exercise caution through at least early
Saturday morning. Weather conditions will improve by the upcoming
weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 78 89 77 / 80 60 70 30
STT 88 78 88 78 / 70 80 70 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
511 AM AST Fri Oct 16 2020

.SYNOPSIS...

A Flash Flood Watch still in effect for Puerto Rico and the U.S.
Virgin Islands through Friday evening. A tropical wave, moving
across the local waters, will interact with a TUTT-low, resulting
in active-weather across the region. Periods of moderate to heavy
rainfall could trigger flash and urban flooding and mudslides
along steep terrains. Tropical moisture will continue across the
islands on Saturday. Conditions are forecast to improve late
Saturday night into Sunday as a mid- to upper- level ridge builds
aloft.

&&

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

An upper-level low will continue to promote instability aloft. At
the surface, a tropical wave will move across Puerto Rico and the
U.S. Virgin Islands, and will bring above normal tropical
moisture over the area. Total precipitable water derived from
GOES-East is above two inches. The tropical disturbance will
promote an east-southeasterly wind flow today. Therefore, an
active weather day is expected today across the islands of Puerto
Rico and the U.S. Virgin Islands.

A Flash Flood Watch remains in effect for all Puerto Rico and the
U.S. Virgin Islands through this evening. Showers will be focus
mainly across the local waters, eastern sections of Puerto Rico
and the U.S. Virgins Islands during the morning hours. As the day
goes, widespread activity will spread westward over the interior
and western section of Puerto Rico. Due to soil saturation and
the likelihood to observe persistent heavy rainfall, the
potential for flash flooding is considered high for the islands.
Also, mudslides across areas of steep terrain are likely with
prolonged heavy rain.

The trailing moisture from today`s tropical wave will continue to
promote rainy conditions on Saturday, especially during the
afternoon hours.

GFS guidance suggests a building ridge at mid- to upper-levels
which is forecast to promote dry air aloft on Sunday. This will
limit vertical development, and the activity if any, will be wind-
driven across the windward sections during the overnight and
morning hours, followed by diurnal induced activity across the
interior and western sections, mainly in PR.

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

GFS and ECMWF suggested a trough at mid- to upper-level moving
across the Atlantic Ocean and near the northeast Caribbean early
next week. Guidances have some discrepancies with the synoptic
pattern at this time, which GFS tends to suggest an induced
surface low meandering north of the islands, and the ECMWF more to
the northeast over the Central Atlantic. Under this pattern,
patches of moisture will move from the Atlantic into the islands
on Monday. Then, leaning toward the GFS solutions, the winds will
become calm to light and variable with a southerly component
Tuesday through Wednesday and a steering wind flow from the
southwest for Thursday. As the low moves northward, winds will
shift more from the southeast by Friday. Under this southerly wind
flow, tropical moisture will move from the ITCZ over the islands,
which GFS suggests TPW around 2 inches Wednesday through the end
of the work-week. Another tropical wave is forecast to move close
to the islands by Friday.

&&

.AVIATION...

VFR conditions are expected thru 16/12Z. A tropical wave will
bring SHRA/VCTS across most of the TAF sites today. Weather
conditions will deteriorate by around 16/14Z, and into the
evening. Therefore, TEMPO due to MVRF conds are likely, mainly at
JSJ and possibly for IST/ISX early this morning. Winds will
continue calm and VRB thru at least 16/13Z, then will return from
the E-ESE at 10-15 knots, with sea breeze variation and
occasional higher gusts.

&&

.MARINE...

The tropical wave will bring an increase in showers and the
potential for thunderstorm development across the local waters
through at least early Saturday morning. Mariners should exercise
caution across the local waters, especially across the Atlantic
and Caribbean Offshore waters and the Anegada Passage due to winds
up to 20 knots and waves between 4 and 6 feet. Elsewhere, seas
will remain at 5 or less.

Marine conditions will improve after the passage of the
aforementioned tropical wave leaving seas below 6 feet and winds
around 15 knots. Although there is plenty of uncertainty, marine
guidance is suggesting the arrival of a northeasterly swell for
early next week.

For the beach goers, there is a moderate risk of rip currents for
the north and southeast beaches of Puerto Rico and Culebra.
Vieques, and the U.S. Virgin Islands have a moderate risk of rip
currents for the eastern and southern beaches.

&&

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 77 88 77 / 50 40 40 20
STT 87 77 87 77 / 80 70 50 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
450 AM AST Sat Oct 17 2020

.SYNOPSIS...

Abundant tropical moisture associated with a tropical wave, now
over the Hispanola, will maintain a high potential for the
development of showers and thunderstorms today. A mid to upper-
level ridge building from the west will replace the TUTT later
today and Sunday. This ridge will promote dry air aloft from this
evening into early next week. A surface-low pressure, which is
monitor by the National Hurricane Center, will linger off to the
north of the local islands through much of the upcoming work-week.

&&

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

An upper-level ridge will build across the local islands through
the short-term period. An improvement in weather conditions is
expected with the high pressure over the area and a drying
pattern. However, lingering surface moisture from yesterday`s
tropical wave will result in showers and thunderstorms throughout
the day. A drier air mass will filter into the region this evening,
limiting shower activity through at least Monday.

That said, the best chance for unstable weather is today.
Widespread shower and thunderstorm activity will affect the
islands, especially from mid-morning into the afternoon hours. As
a result, the Flash Flood Watch was extended for Puerto Rico and
the U.S. Virgin Islands until 8 PM tonight. Yesterday`s rainfall
activity saturated the soils across eastern and interior Puerto
Rico. Therefore, the potential for flash flooding is high across
portions of the interior, west, and east of Puerto Rico. Weather
conditions will improve significantly after this evening and early
Sunday morning continuing into Monday.

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

Once again, both GFS and ECMWF suggested a surface low meandering
north of the islands across the Atlantic Ocean. However, guidances
have some discrepancies with the synoptic pattern and with the
position of this low. The National Hurricane Center is monitoring
this system, and it has a high chance of formation in the next 48
hrs (70 percent) and five days (80 percent). Under this synoptic
pattern, Tuesday seems to be the drier day of the long-term. Winds
are forecast to shift from the south lifting abundant tropical
moisture across the islands of Puerto Rico and the U.S. Virgin
Islands. GFS is suggesting TPW above 2 inches from Wednesday
through the end of the work-week. Keep in mind that there is high
uncertainty about the final weather scenario for the islands.
Another tropical wave is forecast to cross the Lesser Antilles on
Friday, moving near the U.S. Virgin Islands and Puerto Rico around
Saturday.

&&

.AVIATION...

VFR conditions are expected at least until 17/12Z.
Lingering moisture from the previous tropical wave will bring
SHRA/VCTS across most of the TAF sites today. SHRA/TSRA will
increase around 16/14Z, and into the evening. This could result in
MVFR conds, mainly at JSJ and TJPS in the afternoon hours. Winds
will continue calm and VRB thru at least 16/13Z, then will return
from the E-ESE at 10-15 knots, with sea breeze variation and
occasional higher gusts.

&&

.MARINE...

Marine conditions will improve during the next few days with seas
between 2 and 5 feet and winds between 10 and 15 knots. Marine
guidance is suggesting the arrival of two northeast swells for
next week, one arriving around Tuesday evening/Wednesday,
followed by a second one by the end of the work-week.

For the beachgoers, there is a moderate risk of rip currents along
the northern coast of Puerto Rico and in Culebrita. Elsewhere the
risk is low. A similar pattern will continue through at least
Tuesday night when a northerly swell is forecast to increase the
risk into high along the north-facing beaches.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 76 88 78 / 70 50 50 20
STT 88 78 88 76 / 70 40 30 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
423 AM AST Sun Oct 18 2020

.SYNOPSIS...

Surface moisture will slowly erode as a low-pressure system
located about 900 miles northeast from San Juan drifts southward,
pushing a somewhat drier air mass. A mid to upper-level ridge
will build over the northeast Caribbean, promoting a drier air
mass aloft too. The typical weather pattern is forecast for today
and through at least Tuesday. A wet and unstable weather pattern
is possible for the second part of the week, but it`s tight to
the aforementioned surface-low evolution.

&&

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

Showers continued to move across the local and outer waters this
morning; some showers affected the northern and southern areas of
Puerto Rico. A surface low pressure has developed to the southeast
of Bermuda. It is expected to gradually sink southward through the
short-term period, and bring about a northerly wind flow across
Puerto Rico. The northerly wind flow will advect a drier air mass
across the region today. PWAT will continue to fall through Monday
night, with the lowest value 1.09 inches expected Monday afternoon.
Today, showers will move across portions of eastern PR and the
adjacent eastern islands. This afternoon, lingering moisture from
the departed tropical wave and local and diurnal effects will cause
showers and thunderstorms to develop across the interior and
southwestern areas of Puerto Rico. Light east to northeast winds
this afternoon will cause convection to move slowly, leading to
urban and small stream flooding. Soils remain saturated across most
of the area due to previous days rainfall, and additional rainfall
today will cause rivers and small streams to rise quickly.

Monday and Tuesday, the northerly winds will continue to pull drier
air over Puerto Rico and the U.S. Virgin Islands. The lack of
significant low-level moisture and upper-level forcing will bring
fair weather across the region. As 500 MB temperatures warm and low-
level moisture remains below low normal.

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

Once again, both GFS and ECMWF suggested a surface low (which
could be a sub-tropical depression or storm) meandering north of
the islands across the Atlantic Ocean. Although some discrepancy
is present, both models are reaching better consensus respect the
position of this low. The National Hurricane Center (NHC) is
monitoring this system, and it has a high chance of formation in
the next 48 hrs (80 percent) and five days (90 percent). This
system will meanders north of the islands across the Atlantic
Ocean. It will induce a southerly wind flow that would lift plenty
of tropical moisture from the Caribbean Sea into Puerto Rico and
the U.S. Virgin Islands by Wednesday afternoon and through at
least late Thursday night or Friday. GFS-TPW was above 2 inches
through that period. Although there is high uncertainty around
this weather scenario, unstable and wet conditions would remain
possible for the second part of the work-week.

A tropical wave is forecast to cross the Lesser Antilles by
Friday, leaving the islands of PR/USVI in the subsidence ahead of
the wave. The wave axis could move across the U.S. Virgin Islands
and Puerto Rico around Saturday and moving over the Hispaniola by
Sunday when a drier air mass with African dust particles could
reach us.

&&

.AVIATION...

Prevailing VFR conds at all terminals. SHRA will continue
to affect the USVI, PR eastern terminal and terminal sites east
of USVI thru 18/15Z. SHRA/Isold TSRA are expected to develop
across the interior and SW areas of Puerto Rico by 18/18Z, and
diminish by 19/01Z. MVRF conds are possible across the interior
and southwestern areas of PR due to the SHRA/Iso TSRA. Elsewhere,
a few ISO SHRA are possible through 18/19Z. Sfc winds from the
E-NE at 5 to 10 knots, with sea breeze variation by 18/15Z.

&&

.MARINE...

Marine conditions will improve during the next few days with seas
between 2 and 5 feet and winds between 5 and 15 knots. A
northeasterly swell will bring hazardous marine and coastal
conditions across the north-facing beaches of Puerto Rico and the
U.S. Virgin Islands around Tuesday or Wednesday. How much energy
will reach the islands will depend on the intensification of the
surface-low-pressure monitored by NHC, which is north of the
region. A second northeasterly swell is forecast to move across
the islands by the end of the work-week.

For the beachgoers, there is a low risk of rip currents along all
the local beaches, except across Jobos beach where is moderate. A
similar pattern will continue through at least Monday night, when
the risk if forecast to increase.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 77 88 77 / 40 30 20 20
STT 88 77 88 77 / 40 30 20 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
548 AM AST Tue Oct 20 2020

.SYNOPSIS...

Northerly surface winds induced by Tropical Storm Epsilon will
promote relatively dry weather conditions through much of the
short term forecast period. A change in wind direction, more to
the east south east will bring moisture to the forecast area
during the long term period to promote our usual weather pattern.
Tropical Storm Epsilon will continue to generate hazardous marine
conditions during the week.

&&


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

Newly formed Tropical Storm Epsilon, currently 850 miles northeast
of Saint Croix is creating light northerly sfc winds over the area.
The light winds will continue over the next several days as a col
settles over the region. A drier air mass is over the region and
will limit the development of showers and make thunderstorms
unlikely. Nevertheless, scant moisture and local and diurnal effects
will produce showers across portions of interior Puerto Rico. Any
convection will diminish after sunset as the land surface begins to
cool down. During the overnight hours, light to variable winds with
mostly clear skies will prevail. Upper level ridging will remain to
the west for the duration of the period leaving Puerto Rico and the
U.S. Virgin Islands under 20-30 knot northwest flow.

On Wednesday low-level flow will become south to southeast and will
bring back some moisture, however most showers during the overnight
hours will remain over the local waters. During the daytime most
showers will be over the interior and northern parts of Puerto Rico
with mostly isolated showers around the U.S. Virgin Islands.

On Thursday the southerly winds begin advecting drier air back into
the area and shower activity will be reduced. It is then that
precipitable water will reach its lowest point after today.


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

The newly formed Tropical Storm Epsilon will continue to induce a
southerly wind flow through Saturday. A shift more to the east is
expected on Saturday through at least Monday. Models suggest
relatively drier air at the mid levels. The GFS shows a drier
trend at 850 mb at least through Sunday. At the low levels,
shallow moisture embedded in the trade winds is forecast. Thus,
expect the usual passing showers in the morning hours followed by
afternoon convection mainly over portions of western Puerto Rico.

A weak tropical wave is forecast to move across the islands of PR
and USVI on Saturday. The associated moisture will enhance shower
activity across the islands, mainly during the afternoon hours
when it interacts with local effects and diurnal heating. A dry
slot will make its way in to our forecast area by Sunday, but
models are now showing a trough that is expected to quickly reach
our area by the beginning of the next workweek to promote a
wetter weather pattern.

&&


.AVIATION...

VFR conds durg prd xcp for ocnl MVFR CIG at TNCM.
SHRA to dvlp aft 20/17Z interior PR mainly ovr interior sections of
PR with mtn obscurations and MVFR/IFR conds. Sea breezes up to 12
knots. Max winds WNW-NW 25-35 kt btwn FL375-490.

&&


.MARINE...

Marine conditions will continue to deteriorate due to a northerly
swell generated by Tropical Storm Epsilon for the next several
days over the northern nearshore waters of Puerto Rico today. The
swell is forecast to continue to propagate to the south and reach
most of the local waters later tonight into Wednesday. The swell
will cause hazardous marine conditions for all the northern
beaches of Puerto Rico. Seas will steadily increase through
the end of the week with wave heights reaching 8-9 feet tonight.
This swell will also cause life-threatening rip current
conditions. Thus, expect a high risk of rip currents for all the
northern beaches of Puerto Rico for today.

The high tide will be today at 12:07 PM. The San Juan bouy actual
water levels is around 3 inches higher. Thus it is possible that
low level areas could see sea water intrusion. This will be re-
examined later today for the morning forecast package.

&&


.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 89 77 / 20 10 10 10
STT 88 78 88 79 / 20 10 20 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
509 AM AST Wed Oct 21 2020

.SYNOPSIS...

Epsilon is promoting a southerly wind flow, which is forecast to
last through the rest of the work-week. Under this wind flow,
expect near to above-normal high temperatures and afternoon
convection along and to the north of the Cordillera Central each
afternoon. A long-period northerly swell generated by Epsilon will
create hazardous marine and coastal conditions along the Atlantic
Coastline of Puerto Rico and the U.S. Virgin Islands.

&&

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

Winds are forecast to shift to the south to southeast today. Thus, a
change in the weather pattern is expected as the surface winds will
allow moisture to slowly increase throughout the day. The return in
moisture will increase the chance for afternoon convection, mainly
across the interior and northern parts of Puerto Rico, U.S. Virgin
Islands and surrounding waters.

On Thursday, southerly winds will bring back drier air to the
region, which in turn will decrease low-level moisture content
throughout the day. However, the residual moisture will enhance
shower activity across the islands, mainly during the afternoon
hours when it interacts with local effects and diurnal surface
heating. Any convection will diminish after sunset as the land
surface begins to cool down.

Model guidance are suggesting favorable upper-level conditions for
shower and thunderstorm development on Friday. An upper-level trough
strengthens to the northwest and will interact with weak tropical
wave to produce shower and thunderstorm activity mainly across
portions of the northwestern quadrant of Puerto Rico and adjacent
waters.

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

A drier air mass will filter from the east as the tropical wave
moves across Hispaniola. There is a possibility to observe some
African dust particulate, especially by Saturday afternoon.
Although a similar pattern is possible on Sunday, moisture will
increase somewhat across the islands, resulting in more frequent
passing showers, especially across the windward sections.

A mid- to upper-level trough will amplify near the islands of
Puerto Rico and the U.S. Virgin Islands by next week. At the
surface, a surface-induced-trough will cross the islands with an
increase in tropical moisture. Another perturbation will swing by
the region Thursday or Friday. This weather pattern suggests an
unstable weather scenario from Tuesday through Thursday.

&&

.AVIATION...

VFR conds durg the 24 hr prd. Mostly SCT lyrs nr FL025...FL050.
No sig operational wx impacts attm due to direr air mass over the
forecast area. Afternoon convection across SJU possible between
21/16-22z. SFC wnds mainly Light 5-10 kts fm NW- N...bcmg lgt/VRB
to calm aft 21/22Z.

&&

.MARINE...

A long-period northeasterly swell moving across the Atlantic Ocean
will maintain seas between 7 and 12 feet across the Atlantic
Waters and Caribbean Passages. As Epsilon meander well north of
the region, hazardous seas will continue, possibly throughout the
upcoming weekend, as a secondary swell is also forecast to follow.
This northerly swell will produce a High Risk of Rip-Currents,
High Surf Conditions, beach erosion, and minor Coastal Flooding
along the Atlantic Coastline. The Caribbean coastline and south-
facing beaches of Puerto Rico and the U.S. Virgin Islands will
have better coastal conditions.

&&


MARINE...

Marine conditions will continue to deteriorate over the next several
days due to a northerly swell generated by Tropical Storm Epsilon
for the next several days. The swell will cause hazardous marine
conditions for all the northern beaches of Puerto Rico. Seas will
increase to 8 to 10 feet tonight with seas occasionally reaching 12
feet. This swell will also cause life-threatening rip current
conditions. There is a high risk of rip currents for all the
northern beaches of Puerto Rico. There is a Small Craft Advisory for
the northern nearshore and outer Atlantic waters over the next
several days. There is High Surf Advisory for the north- facing
beaches of the region through Thursday afternoon.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 77 90 78 / 40 10 40 20
STT 87 78 86 79 / 10 30 20 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
506 AM AST Thu Oct 22 2020

.SYNOPSIS...Hazardous marine and surf conditions will continue
today since a long-term northeasterly swell generated by Hurricane
Epsilon continues to spread across the regional waters. Epsilon
will also support a light to locally moderate wind flow from the
south to southeast. Under this flow and combined with local and
diurnal effects, shower and possible isolated thunderstorm
development can be expected along the interior and northern
sections of the island. Elsewhere, limited to no shower activity
is expected.


&&

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

Hurricane Epsilon will produce a southerly flow for today. Thus,
warmer temperatures are expected with heat indices reaching the 100s
for parts of the northern coastal areas of Puerto Rico. This wind
flow pattern will also bring back drier air to the region, which in
turn will decrease low-level moisture throughout the day. However,
the residual moisture will enhance shower activity across the
islands, mainly during the afternoon hours when it interacts with
local effects and diurnal surface heating. Upper level dynamics look
favorable for thunderstorm activity, mainly over portions of northern
Puerto Rico and the nearshore waters. Any convection over land will
diminish after sunset as the land surface begins to cool down and
only passing showers could be observe over the regional waters.

Favorable upper-level conditions for shower and thunderstorm
development on Friday. An upper-level trough strengthens and sets to
our northeast. At the low leves, the southerly wind flow will advect
moisture associated with a tropical wave located over the
southwestern Caribbean waters. These features will interact to
produce shower and isolated thunderstorm activity mainly across
portions of the northwestern quadrant of Puerto Rico and adjacent
waters during the afternoon hours. Minor urban and small stream
flooding as well as ponding of waters on roadways and in poor
drainage areas will remain possible in isolated areas with the
heaviest and most persistent rains.

A similar weather pattern is possible on Sunday. Model guidance
suggest an increase in low-level moisture across the islands,
resulting in more frequent passing showers, especially across the
windward sections during the morning hours. Afternoon convection is
expected over the northwestern sections of Puerto Rico. This will
generate showers with isolated thunderstorms that could lead to
minor flooding and ponding of water.

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

Model guidance suggests that a building surface high pressure
over the north Atlantic will maintain moderate to locally strong
trade winds through most of the long-term forecast period. In
terms of shower activity, a trade wind disturbance will enhance
moisture advection and a gradual increase in trade wind showers
between Sunday and Monday. Then, an amplifying mid- to upper-
level trough will sink southward across the eastern Caribbean,
with cutoff low and weak surface-induced trough lingering over the
area through midweek. Increased tropical moisture advection
(model-estimated precipitable water peaking at 2.10 by 18Z on
Tuesday) and somewhat favorable conditions aloft (500 mb
temperatures around -6 degrees C) will enhance shower and
thunderstorm activity through early Thursday. Thereafter, a
relatively drier air mass will filter into the area, decreasing
the chance for shower development.


&&

.AVIATION...Mainly VFR conds durg the 24 hr prd. SCT lyrs nr
FL025...FL050. Possible brief MVFR conds and VCTS at TJPS around
22/08Z due to line of showers approaching from the Caribbean waters.
Afternoon convection will produce VCSH for TJBQ at 22/18Z. SFC wnds
mainly light 5-10 kts fm S-SE...bcmg lgt/vrb to calm aft 22/22Z. No
sig operational wx impacts is expected over the forecast area durg
prd.


&&

.MARINE...A long-period northeasterly swell generated from
Hurricane Epsilon will continue to spread across the regional
waters, resulting in hazardous marine and surf zone conditions
during the next few days. Given that the forecast calls for seas
up to 10 feet with a period up to 13 seconds along with breaking
waves up 14 feet to continue, Small Craft, High Surf, and Coastal
Flooding Advisories, as well as High Rip Current Risk remain in
effect.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 78 91 77 / 40 20 50 50
STT 87 80 88 79 / 20 20 50 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
518 AM AST Fri Oct 23 2020

.SYNOPSIS...Variable weather conditions are expected during the
next few days with the passage of a weak tropical wave today,
followed by relatively drier air on Saturday and an easterly
disturbance along with a surge in moisture by Sunday into early
next week. Thereafter, a generally moist and unsettle weather
pattern is expected with increased deep tropical moisture and
favorable conditions aloft. Improving marine conditions are
expected today, but yet another swell will create hazardous marine
conditions by the end of the weekend into early next week.


&&

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

The southerly wind flow will bring in moisture associated with a
weak tropical wave that will pass by the area to the south later
today. Precipitable water values are forecast be near normal. At the
upper levels, an upper-level trough strengthens and sets to our
northeast will help provide instability aloft. Thus, the combination
of these features will help to support afternoon convection across
northwestern PR and the development of streamers down from El Yunque
and the U.S. Virgin Islands.

As the tropical wave moves away from the forecast area, leftover
moisture, favorable upper leve dynamics and local effects will
result in scattered shower activity across northwestern PR. Isolated
activity is expected elsewhere. A drier airmass will quickly approach
the area late in the afternoon.

Model guidance suggest an increase in low-level moisture associated
with and easterly perturbation across the islands on Sunday. This
will result in more frequent passing showers, especially across the
windward sections during the morning hours. Afternoon convection is
expected over the northwestern sections of Puerto Rico. This will
generate showers with isolated thunderstorms that could lead to
minor flooding and ponding of water.


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

Recent model guidance now suggests that a moist and unsettle
weather pattern will dominate the local weather conditions through
the long term forecast period. First, a trade wind or easterly
disturbance will enhance moisture advection with frequent overnight
and early morning trade wind showers, and the potential for
increased locally and diurnally induced activity on Monday. In the
meantime, an amplifying mid- to upper-level trough will spread
southward across the eastern Caribbean, with weak cutoff low and
surface-induced trough lingering over the region through early
Thursday. Another, but strong cutoff upper level low will quickly
follow, sinking south just northwest of Puerto Rico by Thursday
evening, then drifting westward through early Friday.

To support this scenario, deep tropical moisture with model-
estimated precipitable water above 2 inches by 12Z on Tuesday and
18Z on Wednesday along with favorable conditions aloft with 500
mbar temperatures randing between -6 and -8 degrees C will aid in
the development of shower and thunderstorm activity. Lastly, a
tropical wave is forecast to reach the local islands between
Friday and Saturday. Overall, a deepening surface pressure will
maintain a generally moderate to fresh easterly wind flow through
the period.

This forecast follows closely GFS model guidance. However, there
is medium confidence in this scenario since the ECMWF suggest a
different scenario with relatively drier with ridging aloft by
the end of the workweek.



&&

.AVIATION...Mainly VFR conds are expected to prevail durg the 24 hr
prd. Afternoon convection will produce VCSH for TJBQ/TIST/TISX btwn
23/18-22Z. SFC wnds mainly light 5-10 kts fm S-SE...bcmg lgt/vrb to
calm aft 23/22Z. No sig operational wx impacts is expected over the
forecast area durg prd.


&&

.MARINE...Swell generated by Hurricane Epsilon continues to
diminish, resulting in improved seas. In fact, seas at bouy 41043
have dropped to 5 feet at 11 seconds, while seas at the inner
bouy just north of San Juan, 41053, have dropped to 6 feet at 13
seconds. While this improvement is expected to continue today,
Small Craft Advisories will remain in place through this afternoon
for western-most marine zones. A second pulse is expected to
arrive by the end of the weekend, spreading across the local
waters from the east and creating hazardous seas through early
next week. A high risk of rip currents continues for most north-
and east-facing beaches of Puerto Rico, Culebra, and the US
Virgin Islands.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 79 92 78 / 50 50 30 20
STT 89 79 89 79 / 50 50 20 30