National Weather Service Today's Weather Impact Levels

705
FXCA62 TJSJ 272045
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
445 PM AST Sun Apr 27 2025

.SYNOPSIS...

An unsettled weather pattern is expected to continue through at
least Thursday due to a series of troughs and abundant moisture.
The likelihood of urban and small stream flooding due to strong
showers and thunderstorms, as well as mudslides and rapid river
rises will remain high along with a chance of isolated flash
flooding as well. While there is some uncertainty in the location
and timing of this rain, there is a high confidence of a wet and
unsettled period for Puerto Rico, the Virgin Islands and local
waters. A high rip current risk is in effect for the northern
exposed beaches of Puerto Rico, from Aguadilla to Fajardo and
Culebra through at least late tonight.

&&

.SHORT TERM...Tonight through Tuesday...

Showers and thunderstorms impacted mainly the eastern third of PR
and the US Virgin Islands throughout the morning, producing flash,
river, and urban flooding. Since midnight, the highest radar-
estimated rainfall accumulations ranged from around 1.0 to 2.0
inches, with isolated rainfall amounts of up to 4 inches. Then,
thunderstorms moved across the interior and north central locations
of PR, where estimated ranged between 2 and 3 inches. The maximum
temperatures observed ranged in the mid or upper 80s across the
western half portion of PR, where rain developed around noon.
Today`s winds were mainly from the ESE-SE at 10 mph but gusty near
thunderstorms and with sea breeze variations.

For tonight, we anticipate that today`s afternoon convection slowly
dissipates from the interior and western sections of Puerto Rico
by this evening. However, the unstable pattern will continue due
to the proximity of the deep layer trough and abundant moisture
moving in from the east. Remember that soils are saturated, and
rivers and stream flows are elevated. Thus, any persistent
moderate or heavy rain can lead to flooding issues, including
minor, flash, or river flooding, as well as landslides in steep
terrain. We also expect another round of inclement weather,
spreading from the surrounding waters into the local islands
overnight and tomorrow early morning (Monday), affecting mainly
across the US Virgin Islands and the eastern third of Puerto Rico.

At the beginning of the workweek, we anticipate that the wet and
unstable weather pattern will persist due to the influence of the
mid-to-upper trough and abundant tropical moisture. Although model
guidance indicates a slight decrease in moisture content, it will
remain above normal to average, thus sustaining the wet conditions.
The most significant precipitation activity is expected primarily
during the afternoons and early evenings. Beginning Monday night,
winds will shift from the east to the northeast, resulting in
afternoon showers and thunderstorms concentrating more to the
southeast of the main island. Residents and visitors are advised to
stay informed about the weather and monitor official forecast
updates, particularly because of the ongoing flood risk, which is
the primary concern. The threat of unexpected landslides along steep
terrains is also a concern.

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

./FROM PREV DISCUSSION...Issued at 453 AM AST Sun Apr 27 2025/

A wet and unstable weather pattern will persist through the early
part of the long-term forecast. A surface high-pressure system over
the western Atlantic and a surface low over the central Atlantic
will induce east-northeast winds across the CWA. These northeast
winds will promote low-level convergence over the region,
particularly on Wednesday and Thursday, when the surface low will be
closest to the northeast. Precipitable water content is expected to
remain between 1.7 and above 1.9 inches. These values exceed the
75th and 90th percentiles of the climatological normal, indicating a
continuation of well-above-normal moisture levels for this time of
year.

In terms of instability, the surface low is being induced by an
upper-level cut-off low. These features will lead to a further drop
in 250 mb height fields, cooler 500 mb temperatures, and steeper
lapse rates, sustaining unstable weather conditions capable of
generating deep convective activity. The likelihood of convection
will be highest during the afternoon hours, as high moisture content
and instability combine with surface heating and local effects.

Soils are expected to remain somewhat saturated by Wednesday due to
rains from previous days, with rivers still experiencing elevated
streamflows. Consequently, the flood risk will remain elevated
through at least Thursday, particularly during the afternoon hours.
Quick river rises, river flooding, and landslides are also possible,
primarily across Puerto Rico. In the U.S. Virgin Islands, minor
flooding with brief periods of excessive runoff is possible each day
of the week. Some ridging aloft will bring somewhat more stable
weather conditions by the end of the workweek into the weekend.
Nevertheless, enough low-level moisture could combine with diurnal
heating and local effects during the afternoon to promote convective
activity in localized areas.


&&

.AVIATION...

(18Z TAFS)

SHRA/TSRA will continue to impact the local flying area throughout
the forecast period. Terminals could be affected by this activity,
producing periods of MVFR or even IFR. Thus, TEMPOs will be mainly
required for the following time frames: 18-23z across JBQ/JSJ and 03-
12z near IST/ISX/JSJ. Winds will prevail between 10 and 15 kt,
mainly from the ESE/SE under sea breeze variations, becoming calm to
light and variable after 27/23z, returning from the ESE at around 10
kt after 28/13z with sea breezes.


&&

.MARINE...

Light to moderate east to southeast winds will prevail through at
least tonight, backing from the northeast winds early this week.
A deep layer trough will continue to promote an unstable weather
pattern across the local waters. Thus, showers and thunderstorms
are expected to persist, producing localized hazardous marine
conditions. This unstable and wet pattern will prevail through at
least midweek. A long-period northeasterly swell is spreading
across the Atlantic waters. Therefore, small craft should exercise
caution.

&&

.BEACH FORECAST...

A northeasterly swell of 12-14s is being detected by the CariCOOS
buoys near Rincon, San Juan and Vieques. There is a High Risk of
Rip Currents through at least 6 AM AST tomorrow, Monday, for the
north- facing beaches of Puerto Rico, from Aguadilla to Fajardo,
and Culebra. A High Risk of Rip Currents means that life-
threatening rip currents are likely in the surf zone.

A moderate risk of rip currents is also forecast for tonight for
the beaches of Aguada, Rincon, northern Vieques, northern St.
Thomas, northern St. John and northeastern and eastern St. Croix.
Low risk elsewhere, however, life-threatening rip currents often
occur in the vicinity of groins, jetties, reefs, and piers.

For more information, please refer to the latest Coastal Hazard
Message (CFWSJU) and Surf Zone Forecast (SRFSJU).

Residents and visitors in affected regions should heed warnings,
avoid swimming in these waters, and stay informed about updates
from local authorities.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through late tonight for PRZ001-002-005-
     008-012.

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

$$

SHORT TERM...CAM/ICP
LONG TERM....MRR/GRS

NWS SJU Office Area Forecast Discussion