National Weather Service Today's Weather Impact Levels

597
FXCA62 TJSJ 121700
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
100 PM AST Thu Mar 12 2026

...New SHORT TERM, AVIATION, MARINE, BEACH FORECAST, FIRE WEATHER...

.KEY MESSAGES...
Issued at 100 PM AST Thu Mar 12 2026

* Flooding in urban areas, on roads, and along small streams is
  possible this afternoon across the interior and western Puerto
  Rico due to shower activity and the possibility of isolated
  thunderstorms.

* A drier trend is expected by late Friday into Saturday,
  although localized showers may still develop during the
  afternoon hours due to local effects.

* Increasing winds are expected on Sunday into next week,
   leading to hazardous marine and beach conditions.

* Across the U.S. Virgin Islands, occasional passing trade-wind
  showers will continue, with a drying trend expected by late
  Friday into Saturday.

&&

.Short Term(This afternoon through Saturday)...
Issued at 100 PM AST Thu Mar 12 2026

Today`s observed morning sounding at San Juan (TJSJ) shows low-
level easterly winds of 15 to 25 knots and medium to high moisture
content, with a precipitable water (PWAT) of 1.65 inches.
However, a strong trade-wind inversion is present near the 850mb
level, limiting instability (CAPE of 533 J/kg), which could
inhibit thunderstorm development. Based on this setup, the
available moisture content is expected to support passing showers
that favor the USVI and eastern areas of PR through early this
afternoon, before fueling afternoon showers across western and
southwestern Puerto Rico. Hi-res NBM and ECMWF ensemble models
show rainfall accumulations generally between 1.00 and 2.00 inches
across the interior and western sections, while the USVI and
eastern PR will see lighter amounts ranging from 0.25 to 0.50
inches. Having said that, this morning`s sounding also indicated a
strong upper-level jet of 90 knots, and isolated thunderstorms
cannot be ruled out with this afternoon`s shower activity, and
locally higher rainfall amounts are possible. Leading to urban and
small stream flooding.

A noticeable drying trend will begin late Friday and continue on
Saturday. Global guidance indicates a sharp drop in moisture, with
precipitable water values falling below 1.25 inches and mid-level
relative humidity (700mb-500mb) dropping below 20%. Low-level winds
are also expected to decrease slightly during this time.
Consequently, hi-res precipitation data show a reduction in overall
shower coverage. However, localized afternoon showers will still
produce roughly 0.50-1.50 inches over western Puerto Rico on Friday.
At the same time, the U.S. Virgin Islands and eastern Puerto Rico
remain mostly on the dry side of the model solutions, with minor
rainfall accumulations. Regardless, the proximity of the upper jet
segment can enhance early-morning showers across the USVI and
eastern PR, before a drier air mass moves in later in the day.

By Saturday, the drier airmass will prevail over the region, and
stronger trades are expected to return. Promoting overall breezy and
fair weather conditions across the islands, with limited shower
development. Therefore, expect mostly sunny skies and stable
conditions to start the weekend.

&&

.LONG TERM(Sunday through Thursday)...
Issued at 155 AM AST Thu Mar 12 2026

A broad surface high will move into the western Atlantic and
continue building, promoting increased E to ESE winds. 925 mb wind
speeds will be above normal to briefly 2 standard deviations above
normal, resulting in breezy to locally windy conditions to start the
next week. Unsecured items could blow around. A limited wind risk
will persist during the long term period with an elevated wind risk
possible on Sunday and Monday. Although an upper trough will move
northwest of the islands on Monday and an upper jet over the area
can provide ventilation, 500 mb temperatures will be warmer compared
to the short term period, at -7 to -6 degrees Celsius, while 700 to
500 mb lapse rates will be at below normal to low end normal values
for this time of the year. This will promote more stable conditions
and limit vertical shower development. However, the breezy to windy
E to ESE flow will steer showers and patches of moisture towards
windward sectors with diurnal heating promoting afternoon convective
showers over interior to northwestern PR, as well as lines of
showers towards the USVI, Vieques and Culebra to E and ESE PR.
Patches of moisture arriving towards the islands will maintain
precipitable water (PWAT) values around normal values (with some
variability related to the moist and dry patches), model guidance
suggests that the most broad moisture patch will arrive late Sunday
into Monday. 925 mb temperatures will remain at normal values but
under a general warming trend with less cloud cover and the E to ESE
flow. Patchy fog during the overnight hours at sectors of the
interior. Low concentrations of saharan dust will also be steered
over the region, particularly on Sunday and Monday.

&&

.AVIATION...
(18Z TAFS)
Issued at 1157 AM AST Thu Mar 12 2026

Mainly VFR conditions are expected to prevail across all terminals
through most of the fcst period. However, locally induced SHRA
and possible iso TSTMs over the western interior of PR may lead to
tempo MVFR conds thru 12/22z at TJPS/TJBQ, although VCTS is likely.
Elsewhere, trade wind SHRA will move at times, causing brief periods
of -RA and MVFR cigs. The 12/12z TJSJ sounding indicated east to
east-southeast winds up to 23 kt blo 7000ft.

&&

.MARINE...
Issued at 100 PM AST Thu Mar 12 2026

As the pressure gradient weakens across the northeastern Caribbean,
winds will remain gentle to moderate from the east to northeast
with seas of 3 to 5 feet. These improving marine conditions will
persist through today and into the early part of the weekend.
However, another area of high pressure building across the
northwestern Atlantic by late Saturday into early next week will
tighten the pressure gradient. Winds are expected to increase
(fresh to strong trades) Saturday night into Sunday, resulting in
deteriorating marine conditions with rough and choppy seas across
our regional waters and local Caribbean passages. Small Craft
Advisory conditions are likely from late in the weekend into early
next week, with seas building to around 6 to 8 feet.

&&

.BEACH FORECAST...
Issued at 100 PM AST Thu Mar 12 2026

A moderate risk of rip currents remains in place along the north-
and east-facing beaches of Puerto Rico, Culebra, and St. Croix,
meaning that life-threatening rip currents are possible in the
surf zone tonight. A low risk remains elsewhere, however, keep in
mind that life-threatening rip currents often occur in the
vicinity of groins, jetties, reefs, and piers. At the moment, the
forecast shows this same pattern persisting at least through
Saturday night, followed by deteriorating conditions beginning
Sunday as the moderate risk expands to most beaches and a high rip
current risk likely develops by Monday onward, along with breezy
to windy conditions.

Residents and visitors are encouraged to monitor the forecast for
any updates or adjustments. For additional information and
location-specific rip current details, please visit:
weather.gov/beach/sju.

&&

.FIRE WEATHER...
Issued at 100 PM AST Thu Mar 12 2026

The KBDI in Cabo Rojo slightly decreased to 660 compared to yesterday,
but it is still above the critical fire weather threshold. Guanica
is in 520 and Camp Santiago 374. Before noon, RH values decreased
to low the low 50s in Cabo Rojo and even winds are lighter, some
period of gusts up to 20 mph were registered. For the rest of the
afternoon, RH values should increase as afternoon convection is
expected across western PR, keeping the risk low. At this time an
RFD will not be issued, but we encourage partners to continue
monitoring conditions in the coming days, particularly on Saturday
as a drier airmass is expected to arrive.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM/AVIATION...DS
LONG TERM...MRR
MARINE/BEACH/FIRE...YZR

NWS SJU Office Area Forecast Discussion