726
FXCA62 TJSJ 282035
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
435 PM AST Fri Jun 28 2024


.SYNOPSIS...

The passage of a tropical wave and a trade wind pattern will bring
afternoon convection over western Puerto Rico and downwind of the
smaller islands through the weekend. Invest 95L will start to
impact the local area from late Monday night through Tuesday as it
moves south over the Caribbean waters. Continue to monitor the
forecast as this event unfolds.

&&

.SHORT TERM...Tonight through Sunday...

Expect a gradual increase in moisture content through the night into
tomorrow as as a tropical wave moves across the eastern Caribbean,
bringing patches of moist air into the region under a surface trade
wind flow. Mostly easterly flow through the lower to mid-levels
will allow sea breeze convergence and daytime heating to bring
afternoon convection across western Puerto Rico with eastern
sections also receiving showers. Urban and small stream flooding
is possible with this activity. It will be hot again across the
islands with maximum temperatures reaching the low 90s across the
lower elevations with heat indices ranging between 108F- 112F
before the onset of afternoon convection.

Trailing the tropical wave there is a Saharan Air Layer with
moderate amounts of Saharan dust that should cause hazy skies across
the USVI by Saturday evening, spreading across the rest of the area
through Sunday. Therefore, a decrease in shower activity is expected
on Sunday in general. However, afternoon convection will still
develop over western PR with thunderstorms likely.

&&

.LONG TERM...Monday through Friday...
/from previous discussion/
By early next week, drier air will filter across the islands,
with suspended Saharan dust particulate engulfing the area. This
will promote hazy skies and limit the potential for shower
activity throughout most of the day. Although isolated to
localized scattered showers cannot be ruled out, particularly
during the afternoon hours, excessive heat threat will continue as
southeasterly winds prevail, advecting warm temperatures across
the northeastern Caribbean and combining with the Saharan Air
Layer.

The rest of the long-term forecast continues to appear active. A
tropical wave (Invest 95L or AL95) located several hundred miles
west-southwest of the Cabo Verde Islands is being monitored by the
National Hurricane Center (NHC), with a high potential of developing
into a tropical depression or tropical storm in the next day or so.
However, model guidance suggests that this system will stay south of
the local islands, crossing the Caribbean Sea by late Monday night
through Tuesday. Despite the expected system remaining over the
Caribbean waters, the broad moisture field will engulf the forecast
area, increasing the potential for squally weather. Therefore, as
AL95 approaches, expect increased cloudiness and deteriorating
conditions with heavy showers and gusty winds. A limited to elevated
flooding threat can be anticipated, particularly as it interacts
with the Cordillera Central in Puerto Rico.

Another tropical wave behind AL95, centered a few hundred miles
south-southwest of the Cabo Verde Islands, is also being monitored
by the NHC. Although significant development of this system is not
anticipated at the moment. Model guidance suggests this tropical
wave will also move south of the islands. Similarly, although a
direct impact is not anticipated, the moisture field will again
cover the forecast area, maintaining wet and unstable weather
conditions from Thursday through the end of the workweek.

Forecast confidence is low to moderate regarding the impact of both
tropical waves on the forecast area by next week. Therefore,
continue to monitor the forecast, as slight deviations in the tracks
of AL95 and the tropical wave behind it could change the expected
impacts across the local islands.


&&

.AVIATION...

(06Z TAFS)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, SHRA/TSRA expected to develop
over the interior of PR, which may cause MVFR conds in and around
TJPS/TJSJ/TJBQ btw 28/17z-22z. Across the USVI terminals, mostly
VCSH with brief periods of -SHRA can be expected. E-ENE winds at 12-
16 kt with stronger gusts and sea breeze variations aft 28/14z.

&&

.MARINE...

A surface high pressure over the central Atlantic will
promote light to moderate east-southeasterly winds. Trade wind
showers will move across the regional waters from time to time due
to a tropical wave moving south over the Caribbean Waters by
Saturday. A surface low with a high potential of developing into a
tropical cyclone, according to the National Hurricane Center,
will move into the Caribbean Sea by late Monday night into
Tuesday, likely deteriorating marine conditions.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

ERG/MMC/RC