382
FXCA62 TJSJ 140908
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
508 AM AST Wed May 14 2025

.KEY MESSAGES...

* An approaching trough and a surge in tropical moisture will
  result in a gradual transition to a wet and unstable weather
  pattern, with and increased flooding risk, through the end of
  the workweek and the weekend.

* Breezy to locally windy conditions will persist for the next
  few days.

* Increasing winds will result in choppy to rough seas and a
  moderate risk of rip currents through the end of the workweek.

&&

.SHORT TERM...Today through Friday...

Overnight conditions were relatively quiet across the region.
However, an increase in cloud cover and trade wind showers was
observed as a plume of tropical moisture continued to spread across
the area. Strengthening easterly winds allowed some of these showers
to push farther inland, reaching the central interior of Puerto
Rico. Radar estimates indicated isolated rainfall totals of around
three-quarters of an inch, mainly over eastern Puerto Rico. Winds
ranged from 5 to 15 mph in windward areas, while lighter and more
variable conditions prevailed inland and across leeward areas.
Minimum temperatures dropped to around 60F in higher elevations,
with the local island remaining near 80F.

Looking ahead, a gradual transition to a wetter and more unstable
weather pattern is expected through the end of the week, with Friday
likely being the most active day. A broad high-pressure system over
the North Atlantic will maintain breezy to locally windy conditions
today, steering trade wind showers across windward coastal areas,
especially overnight and early mornings. Meanwhile, a weakening
ridge and an approaching trough from the west-northwest will also
interact with a surge of tropical moisture from the southeast. As a
result, precipitable water values will climb sharply, from below 1.5
inches to above 2.0 inches by tonight, promoting deep-layer moisture
and an increasingly humid, unstable atmosphere.

Rainfall activity today is expected to remain relatively localized,
mainly affecting northwestern Puerto Rico. However, as moisture
levels and upper-level support improve, showers and thunderstorms
are forecast to become more widespread and intense on Thursday and
Friday. With PWAT values peaking near 2.2 inches and 500 mb
temperatures dropping to around -8 C, conditions will be favorable
for moderate to heavy rainfall periods. While Saharan dust and cloud
cover may limit some convective development, the overall risk for
urban and small stream floodingand potentially isolated flash
floodingwill increase. A Hydrologic Outlook may be issued in the
coming days, with a Flash Flood Watch possible if forecast
confidence continues to grow. Residents and partners are encouraged
to stay informed and monitor future updates, including the
Experimental Graphical Hazardous Weather Outlook for evolving hazard
information.

.LONG TERM...Saturday through Wednesday...

A wet and unstable weather pattern is forecast Saturday through
early next week. A deep layered trough, currently over the western
Caribbean and western Atlantic, will gradually move eastward
towards the local islands, this feature will promote more
favorable conditions for widespread shower and thunderstorm
activity during the weekend. A surface trough will also develop,
also providing instability and promoting, along with a surface
high over the central to eastern Atlantic, light east- southeast
to southeast surface flow over the region to start the period.
These features will converge with deep tropical moisture that will
also be over the region and will continue to arrive from the
east- southeast, with current model guidance showing a completely
moist atmospheric profile, possibly being somewhat confined to
below 500mb by late Sunday and into early next week. By Saturday,
current model guidance continues to indicate precipitable water
(PWAT) values around 2.25 inches over the islands, above normal
values for this time of the week. A slight decrease in PWAT values
is forecast at times during the period but will increase again to
around 2 inches. A limiting factor for this activity could be
Saharan Air Layer that could also reach the islands this weekend.
Although PWAT values will continue to be elevated, the deep layer
troughs influence will not be as pronounced Tuesday and Wednesday.
Widespread showers and thunderstorms are forecast particularly
over the eastern region and interior PR and with already saturated
soils and elevated streams, there is an increased risk of urban
and small stream flooding, flash flooding, river rises and debris
flow in steep terrains. Up to an elevated flooding risk is
forecast during these days. Further monitoring will continue and
a significant flooding threat may be added and a Hydrologic
Outlook may be issued soon, a Flash Flood Watch is also possible.
Stay tuned for any updates.

&&

.AVIATION...

(06Z TAFs)

Generally, VFR conditions are expected across all TAF sites,
though brief MVFR conditions are possible due to trade wind
showers and afternoon SHRA/TSRA. While the chance for MVFR
conditions will persist at TJSJ and USVI terminals, TJBQ and TJPS
may experience MVFR conditions after 14/16Z and 14/22Z,
respectively. Easterly winds will range from 510 knots,
increasing to 1520 knots after 14/13Z, before becoming light and
variable after 14/22Z. Higher gusts are possible in and near
SHRA/TSRA.

&&

.MARINE...

A broad surface high pressure over the Central Atlantic will
promote breezy easterly winds that will result in choppy
conditions across the offshore waters. A Small Craft Advisory is
in effect for the Offshore Atlantic and Anegada Passage through at
least this evening due to seas building up to 6 to 7 feet. Small
Craft Should Exercise Caution over most of the other local waters.
A deep trough will promote an unsettled weather pattern with a
high chance for thunderstorm development from Thursday afternoon
onward, resulting in locally higher winds and seas.


&&

.BEACH FORECAST...

There is a moderate risk of rip currents today for the northern
to eastern beaches of Puerto Rico, from Aguadilla to Ceiba, as
well as for southeastern Puerto Rico, sectors of southwestern
Puerto Rico, and most of Culebra, Vieques, St. Croix, St. Thomas
and St. John. In general, a low to moderate risk of rip currents
will persist through the workweek, before becoming mostly low on
Saturday and Sunday. 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.

&&

.HYDROLOGY...

Abundant tropical moisture and a lingering trough will enhance the
potential for showers and thunderstorms across Puerto Rico and the
Virgin Islands by the end of the workweek and into the weekend.
Soils are saturated (with soil saturation > 80%), and streams are
running at normal to above-normal levels, heightening the risk of
flooding. Rainfall could range from 2-4 inches each day, with the
highest risk expected on Friday and Saturday. As winds weaken over
the weekend, any rainfall that develops will persist longer,
increasing the risk of mudslides, rapid river rises, and isolated
flash flooding. While there is some uncertainty related to increased
cloud cover and Saharan dust particles limiting rainfall
development, the overall period is expected to remain unsettled.
Residents and visitors are urged to stay informed for updates.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...Small Craft Advisory until 6 PM AST this evening for AMZ711-723.

&&

$$

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