087
FXCA62 TJSJ 062109
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
509 PM AST Thu Mar 6 2025

.SYNOPSIS...

Marginal instability and above normal moisture will result in
another active afternoon tomorrow. Tonight, an approaching frontal
boundary will continue interacting and weakening a surface-
induced trough, increasing shower activity. A more stable weather
pattern is forecast during the weekend. However, the typical
diurnal rain pattern will affect the PR and USVI. A northwesterly
swell is expected to arrive this weekend, likely creating
hazardous marine conditions across the Atlantic waters and
northern local passages and promoting a high risk of rip currents
for exposed beaches..

&&

.SHORT TERM...Tonight through Saturday...

Showery weather affected the southeast coast of Puerto Rico and the
Virgin Islands this morning. This activity resulted in rainfall
maximum amounts between 0.25 and 0.75 inches throughout the
morning. Then, shower activity diminished around mid-morning into
the afternoon. However, rain activity returned by the afternoon
across the north-central and northwest and across St Thomas and St
John. Maximum temperatures were in the upper 80s along the
coastal areas.

As the winds shift to southerly winds, induced afternoon convection
will form along the interior and northern sections, where ponding of
water and isolated urban flooding will form. Showers will slowly
dissipate over PR through the evening, moving into the surrounding
waters and the US Virgin Islands overnight.

This evening, an approaching frontal boundary will continue
interacting and weakening a surface-induced trough. As the shearline
approaches, winds will become calm to light and variable due to a
col region developing over the islands. The available moisture and
the weak steering wind flow, with a possible northerly wind
component during the afternoon hours, will promote showers to
develop across most mainland PR. If this weather pattern holds, we
can see excessive rainfall, resulting in urban or river floods,
especially by Friday afternoon. Rain activity should diminish by
Friday afternoon over the Virgin Islands, where an increase in
sunshine should materialize.

A more stable weather pattern will build over the Northeast
Caribbean by the weekend. However, the typical diurnal rain pattern
will affect the PR and USVI regions. In addition, a northerly swell
will promote life-threatening rip currents along the north-facing
beaches of the islands.

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

./FROM PREV DISCUSSION...Issued at 509 AM AST Thu Mar 6 2025/

The long-term period will be mainly characterized by more stable
conditions. A mid-to upper-level ridge will remain in place at least
through Tuesday or mid week, suppressing deep convective development
across the region. At the surface, east-southeast trade winds will
dominate throughout the period due to a broad surface high pressure
system across the Atlantic. Based on the latest model guidance,
precipitable water values will remain in the below normal range
through at least Tuesday. As a result, shower activity, if any, is
expected to follow a more typical pattern, where we observe isolated
showers moving across windward coastal areas during the night and
early morning hours, followed by localized shallow convection
developing across western and interior sections of Puerto Rico in
the afternoons. At the moment, no significant rainfall accumulations
or widespread flooding concerns are expected. By midweek onwards,
precipitable water values are expected to slightly increase to
seasonal levels as patches of moisture in the trades move across the
forecast area, and a weak upper-level trough and its associated
frontal boundary approach the Caribbean from the northwest.

Overall, a quiet weather pattern is expected through most of the
period, with Wednesday and Thursday being the days with the best
chances of rain, especially in the afternoon hours across portions
of western Puerto Rico. However, no significant flooding concerns
are anticipated at this time. Daytime temperatures are expected to
remain in the mid to upper 80s along coastal and lower elevation
areas, while temperatures in the mountains will range from the mid
70s to lower 80s.

&&

.AVIATION...

VFR conditions will mainly prevail across all TAF sites. However,
SHRA/TSRA will develop across central and northern PR through
06/23z, affecting primarily JSJ/JBQ, where brief MVFR conditions
will develop. Also, IST will be impacted by SHRA/TSRA. Expect winds
from the ESE/SE or more S between 5 and 15 kt through tomorrow. Calm
to light, and variable winds are expected overnight, ranging between
5 and 10 kt with sea breeze variations after 07/13z. SHRA/TSRA will
form once again tomorrow.

&&

.MARINE...

A fading northerly swell will continue to spread across the
Atlantic waters keeping wave heights around 5 to 6 feet through at
least today. A frontal boundary approaching from the western
Atlantic will continue to weaken the pressure gradient associated
with the broad surface high pressure extending from the eastern to
central Atlantic, resulting in light to moderate southerly winds
tonight. By Friday, winds will become even lighter while turning
from the east to northeast due to the influence of a col region.
Additionally, a long- period northwesterly swell is expected to
arrive next Saturday, likely deteriorating marine conditions
across the Atlantic waters and northern local passages

&&

.BEACH FORECAST...

A High Risk of Rip Currents remains in effect for the north
oriented beaches of Puerto Rico, from Aguadilla to Fajardo, until
6 PM AST this evening due to a fading northerly swell.

For tonight and tomorrow, a moderate risk of rip currents will be
in effect for the north oriented beaches of Puerto Rico, from
Rincon and Fajardo, and Culebra, as well as for the easternmost
beaches of St. Croix. Low risk elsewhere, however, life-
threatening rip currents often occur in the vicinity of groins,
jetties, reefs, and piers.

A long- period northwesterly swell is expected to arrive next
Saturday, likely promoting a High Risk of Rip Currents along
exposed beaches.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk until 6 PM AST this evening for PRZ001-002-
     005-008.

VI...None.
AM...None.
&&

$$

SHORT TERM...LIS/CAM
LONG TERM....YZR/MRR