761
FXCA62 TJSJ 201049 CCA
AFDSJU

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
649 AM AST Sun Apr 20 2025

.SYNOPSIS...

An increased flood risk continues this morning, especially in
areas with saturated soils, mainly across northern and central
Puerto Rico. Mid-to-upper-level and surface-induced troughs will
continue to dominate through early this afternoon, maintaining
favorable conditions for shower and t-storm development. A
significant pattern shift begins later this afternoon and tonight
as a drier air mass moves in. Marine and coastal conditions are
also deteriorating. Small Craft Advisories are, or will soon be,
in effect for the offshore Atlantic waters, the Mona Passage & the
nearshore waters of N and NW Puerto Rico. A High Risk of Rip
Currents is in effect today for the north-oriented beaches of
Puerto Rico, from Rincon to Fajardo, and Culebra.

&&

.SHORT TERM...Today through Tuesday...

Radar and satellite data revealed an active 1824 hours, driven
by a mid-to-upper-level trough interacting with a surface trough.
Widespread showers and thunderstorms developed under moist
conditions and north-northeasterly trade winds. The heaviest
rainup to 8.3 inchesfell over parts of Vega Baja, Manati,
Morovis, and Ciales, with another peak near the Corozal-Orocovis
line. This led to minor to moderate river flooding and road
closures along the Rio Grande de Manati and Rio Cibuco. Multiple
Flood Advisories and Warnings were issued. Overnight lows ranged
from 60F in the mountains to the mid-70s in eastern PR and the
USVI, with light to moderate N-NE winds.

The mid-to-upper-level and surface-induced troughs will continue
to dominate through early this afternoon, keeping conditions moist
and unstable with a high chance of showers and thunderstorms.
Strengthening north to northeasterly winds, driven by a surface
high to the west-northwest, will enhance moisture advection and
increase trade wind showers. A weak or absent trade wind cap will
support vertical cloud growth, while unusually cool mid-level
temperatures (around -8 to -9C) will sustain instability. Despite
a gradual drop in precipitable water, values between 1.4 and 1.6
inches will continue to support efficient rainfall.

A significant pattern shift begins later this afternoon and
tonight as a drier air mass moves in, driven by increased
convergence and subsidence aloft behind a departing trough.
Precipitable water may drop to 0.9 inches by Monday, while rising
500 mb temps (near -5C) and a redeveloping trade wind cap will
stabilize the atmosphere and limit convection. As a result,
expect fewer showers, breezy conditions, and cooler-than-normal
temperatures to start the week, supported by persistent N-NE
winds and lower 925 mb temps.

An increased flood risk continues this morning, especially in
areas with saturated soilsmainly across northern and central
Puerto Rico. Localized flash flooding, lightning, gusty winds,
and non- thunderstorm wind hazards are possible. See the
Experimental Graphical Hazardous Weather Outlook for details:
https://www.weather.gov/erh/ghwo?wfo=sju.

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

Current model guidance has precipitable water values (PWAT) at
0.90 to 1.10 inches by midweek, below normal values. By Wednesday,
the mid to upper level trough that has been affecting the islands
will be well northeast of the islands, and will gradually
dissipate by Thursday. A surface trough, however, will continue to
move towards the islands and eventually cross the region,
promoting east- northeasterly steering flow on Wednesday,
gradually backing to become east-southeasterly by Thursday and
into the weekend. A notable increase in PWAT values is forecast by
early Friday as abundant moisture from the starts to enter the
region behind the surface trough. By Friday morning, eastern PR is
forecast to have more than 1.5 inches of PWAT, with values
gradually increasing eastward and St. Croix having around 2.0
inches. This moisture surge will continue into the weekend with
PWAT values ranging from 1.8 to 2.0 inches by Sunday, above normal
values for this time of the year. Most available moisture will be
confined to below 700 mb to start the period and through at least
late Friday. In general, weather conditions are forecast to
become increasingly more humid as the workweek progresses.
Overnight and morning showers are still forecast over windward
areas while afternoon convection will still occur over sectors of
western PR, depending on the prevalent steering flow each day. The
increase in moisture to end the workweek and into the next
weekend can increase the coverage of this activity. 925 mb
temperatures are forecast to be at below to normal values by
midweek, gradually climbing due to east-southeast flow during the
second half of the workweek.

&&

.AVIATION...

(06Z TAFs)

SHRA/Iso TSRA will likely cause brief MVFR to IFR conditions at all
TAF sites, with the most significant impacts at TJSJ, TJBQ, and
USVI terminals through the next 12 hours. VFR conds expected after
20/20Z. Northeast winds at 1015 knots, increasing to 1520 knots
with higher gusts after 20/14Z. Gusty winds near showers and
storms are possible. Winds will gradually ease to 515 knots by
20/23Z.

&&

.MARINE...

A surface high pressure system over the western Atlantic will
continue to push remnant showers of a past frontal boundary across
the region while a nearby mid to upper level trough and a surface
trough produces favorable conditions for their development this
morning. This will lead to increased showers and thunderstorms
across the local waters. Increasing northeasterly winds and a
weak northerly swell will maintain hazardous marine conditions
into early next week.

A Small Craft Advisory is in effect for the offshore Atlantic
Waters, Mona Passage, and coastal waters of northern and
northwestern Puerto Rico. Conditions will be hazardous to small
craft in these areas. Inexperienced mariners, especially those
operating smaller vessels, should avoid navigating in hazardous
conditions. For more information, please refer to the latest
Marine Weather Message (MWWSJU) & Coastal Waters Forecast
(CWFSJU).

&&

.BEACH FORECAST...

Today, increasing winds and a weak northerly swell will deteriorate
coastal conditions mainly at the northern coasts of Puerto Rico
and Culebra. A High Risk of Rip Currents is in effect for the
north- oriented beaches of Puerto Rico, from Aguadilla to Fajardo,
through at least early Tuesday. A High Risk of Rip Currents is
also in effect for the beaches of Rincon, Aguada and Culebra,
through at least early tomorrow, Monday. A High Risk of Rip
Currents means that life-threatening rip currents are likely in
the surf zone.

A moderate risk of rip currents continues today and tonight for
several beaches of St. Thomas, St. John, St. Croix, SW Puerto
Rico and Vieques. A moderate risk of rip currents means that
life- threatening rip currents are possible in the surf zone. Life-
threatening rip currents often occur in the vicinity of groins,
jetties, reefs, and piers.

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.

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

&&

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

     High Rip Current Risk through late tonight for PRZ010-012.

VI...None.
AM...Small Craft Advisory until 6 AM AST Tuesday for AMZ711-741.

     Small Craft Advisory until 6 AM AST Monday for AMZ712-742.

&&

$$

SHORT TERM...ICP
LONG TERM....MRR