020
FXCA62 TJSJ 072102
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
502 PM AST Mon Apr 7 2025

.SYNOPSIS...

Variable, seasonal weather will gradually shift to a wetter
pattern, with lighter winds and warmer-than-normal temperatures.
Patches of low-level moisture from the east are forecast to move
over the region tonight into Tuesday. A northeasterly long-
period swell, detected by offshore buoys, will arrive tomorrow
night, deteriorating marine and coastal conditions and result in a
Small Craft Advisory and a High Risk of Rip Currents.

&&

.SHORT TERM...Tonight through Wednesday...

This morning, mostly clear skies prevailed across Puerto Rico and
the U.S. Virgin Islands. By the afternoon, partly cloudy conditions
developed over the interior, eastern, and western sections of Puerto
Rico, with some convective showers and isolated thunderstorms
developing over NW PR. The doppler radar detected above three
quarters of an inch over Aguada, Moca, San Sebastian and Lares.
San Sebastian saw the highest, radar estimated, accumulations
with around an inch and a half. Winds remained from the east at 15
to 20 mph. Maximum temperatures reached the mid to upper 80s to
around 90 along the coast, while mountainous areas remained in the
70s to low 80s.

The latest model guidance indicates that a surface high pressure to
the north will gradually strengthen over the central Atlantic during
the short-term period. As a result, moderate to locally fresh
easterly winds are expected to persist over the next few days.
Additionally, patches of low-level moisture and showers from an old
frontal boundary approaching from the east are forecast to move
across the region tonight into Tuesday.

Precipitable water values are expected to rise to around 1.60 inches
by midweek. By late Wednesday, an induced low-level trough is
anticipated to develop over the east/southeastern Caribbean,
bringing continued moisture pooling near the local area. However, an
upper-level ridge will build over the islands, and 500 mb
temperatures are expected to warm to around -5C. This will likely
suppress significant thunderstorm development, though afternoon
showers are still expected.

.LONG TERM...Thursday through Monday...
./FROM PREV DISCUSSION...Issued at 446 AM AST Mon Apr 7 2025/

The wetter pattern may start earlier than expected. Latest model
guidance shows an increase of moisture content in the low to mid
levels by late Thursday into Friday. This is due the high surface
pressure in the Western Atlantic dragging the remnants of another
frontal boundary and an induced low-level trough southeast of the
Caribbean. PWAT values will continue increasing to above
climatological normals (1.7 - 1.8 inches). The mid-level ridge is
expected to move over the CWA and linger for the next few days,
once again warming 500 mb temperatures (around -4 Celsius) and
inhibiting deep convection activity. However, enough low to mid
level moisture will promote frequent moderate to locally strong
showers each day, moving along windward sections in the nights and
early mornings, then enhance over interior and western/northwestern
PR in the afternoons. Expected rainfall accumulations will result
in mostly ponding of water in roadways and poorly drained areas,
promoting urban and small stream flooding. As the high surface
pressure migrates eastward and a polar trough deepens, a col
area will move close to the region by late Monday, slowing winds
and favoring the development of showers across the region.

With the east-southeasterly flow dominating the period, warmer and
moist air will filter into the region, increasing temperatures to
above normal for this time of the year. However, extreme heat danger
will remain low.

&&

.AVIATION...

(18Z TAFs)

Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. East winds will persist at
14-18 kt with sea breeze variations and stronger gusts,
diminishing at 10 knots at around 07/23Z. VCSH will be present at
08/15Z near TIST & TJPS.

&&

.MARINE...

A broad surface high pressure over the western Atlantic will
continue to promote moderate to locally fresh easterly winds for
the next few days. As a result, Small Craft Should continue to
Exercise caution. A northeasterly long period swell will arrive
later tomorrow night, increasing seas and deteriorating marine
conditions throughout the rest of the workweek. A Small Craft
Advisory will be in effect for the offshore Atlantic Waters and
the Anegada Passage from tomorrow evening through Wednesday
evening. For more information, please refer to the latest Coastal
Waters Forecast (CWFSJU) and the latest Marine Weather Message
(MWWSJU).

&&

.BEACH FORECAST...

For tonight, a moderate risk of rip currents continues for
northern/eastern PR, Culebra, and the U.S. Virgin Islands. A
northeasterly long period swell has been detected by offshore
buoys and is expected to arrive late tomorrow, Tuesday, increasing
seas and deteriorating marine and coastal conditions throughout
the rest of the workweek. A high risk of rip currents is forecast
for Tuesday night into Thursday. For more information, please
refer to the latest Surf Zone Forecast (SRFSJU).

Rip currents are powerful channels of water flowing quickly away
from shore, which occur most often at low spots or breaks in the
sandbar and in the vicinity of structures such as groins, jetties
and piers. They can sweep even the best swimmers away from shore
into deeper water, where it becomes difficult to return to safety.
Heed the advice of lifeguards, beach patrol flags and signs.

If you become caught in a rip current, yell for help. Remain
calm, do not exhaust yourself and stay afloat while waiting for
help. If you have to swim out of a rip current, swim parallel to
shore and back toward the beach when possible. Do not attempt to
swim directly against a rip current as you will tire quickly.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...Small Craft Advisory from 6 PM Tuesday to 8 PM AST Wednesday for
     AMZ711-723.

&&

$$

SHORT TERM...MMC/ICP
LONG TERM....MRR
AVIATION.....LIS