848
FXCA62 TJSJ 280859
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
459 AM AST Fri Jun 28 2024

.SYNOPSIS...

The primary concern for the short-term period will continue to be
heat, at least through this weekend. Additionally, some suspended
Saharan dust particulate is expected by tomorrow and will persist
through early next week, contributing to hazy skies and a
moderate to localized high heat risk. Afternoon convection is
likely every day, mostly over western Puerto Rico. 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...Today through Sunday...

Trade wind showers increased overnight across the regional waters
and over portions of the islands. The Doppler radar estimated around
a tenth of an inch in St. John and half an inch over northeastern
Puerto Rico. Minimum temperatures were from the upper 60s to mid 70s
across the higher elevations, and from the upper 70s to low 80s
across coastal municipalities. Winds were light from the east to
northeast.

A gradual increase in moisture content is expected through Saturday.
Today, a trade wind perturbation will continue to induce scattered
showers across the local waters and enhance afternoon shower and
thunderstorm activity mainly across the interior and western
sections of Puerto Rico. A northeasterly component in the winds in
combination with the sea breeze convergence and daytime heating will
favor showers over the SW quadrant of PR. Urban and small stream
flooding is expected with this activity. It will be hot again across
the islands and a Heat Advisory (NPWSJU) was issued for St. Croix,
and for the north, south, and western coastal counties of Puerto
Rico. Maximum temperatures should reach the low 90s across the lower
elevations with heat indices ranging between 108F-112F before the
onset of afternoon convection.

A wind shift from the east to southeast is expected on Saturday as a
tropical wave moves across the eastern Caribbean. Shower activity
will increase in coverage as well as thunderstorms across the local
waters. Urban and small stream flooding will remain as the main
weather hazard, particularly across the NW quadrant of PR on
Saturday afternoon. Trailing the 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.

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

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. Another tropical
wave 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.


&&

.BEACH FORECAST...

There is moderate risk for the island of St. Croix. Elsewhere, the
risk is low. Deteriorating conditions is expected by early next
week, particularly across south-facing beaches as Invest 95L
approaches and moves south of the area across the Caribbean Sea.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ001-003-005-007-008-010-011.

VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for VIZ002.

AM...None.
&&

$$

SHORT TERM/AVIATION...DSR
LONG TERM/MARINE/BEACH....CVB