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794
FXCA62 TJSJ 120555
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
155 AM AST Thu Mar 12 2026

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

.KEY MESSAGES...
Issued at 135 AM AST Thu Mar 12 2026

* Ponding of water is anticipated with the expected increase
  shower activity across Puerto Rico.

* Slightly drier trend by late Friday into Saturday, but showers
  may develop during the afternoon hours.

* Lighter winds are expected through early Saturday, increasing
  on Sunday, leading 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
  and Saturday.

&&

.Short Term(Today through Saturday)...
Issued at 135 AM AST Thu Mar 12 2026

Overnight conditions were generally calm, with passing showers
affecting portions of northern to northeastern Puerto Rico, Vieques,
Culebra, and the U.S. Virgin Islands under partly cloudy skies.
Rainfall accumulations were mostly light, generally between 0.10
and 0.30 inches, with localized accumulations reaching 0.50 inches
over the Caribbean waters. Winds remained light and variable,
increasing slightly in the heaviest shower activity. Temperatures
stayed in the upper 60s to mid-70s along coastal areas and from
the low to upper 60s across interior and mountainous areas.

Today into Friday will be the wettest days of the short-term period,
before conditions gradually trend drier late Friday into the
start of the weekend. The latest model guidance indicates
precipitable water values between 1.50 and 1.75 inches through
Friday, decreasing to around 1.20 inches by Saturday, which is
near normal values for this time of year. The causes of this wet
pattern will be an upper-level trough and an induced low-level
trough, which will enhance shower activity and produce periods of
moderate to heavy rainfall. The primary hazard will be urban and
small-stream flooding, especially today, as weak steering winds
will allow showers to move slowly, particularly across mountainous
areas. Gusty winds may accompany the strongest activity.
Meanwhile, 500 mb temperatures around 10 C would typically
support some lightning potential; however, recent similar
conditions have produced little to no lightning activity, so the
probability of thunderstorms today remains low to near zero
despite the abundant atmospheric moisture.

By late Friday into Saturday, drier air and more stable conditions
will gradually spread across the region as precipitable water
values return closer to seasonal levels, as a high pressure
system build over the Atlantic. Nevertheless, trade wind showers
will support afternoon showers, mainly across western Puerto Rico,
as easterly winds will dominate the forecast area.

&&

.Long Term(Sunday through Thursday)...
Issued at 135 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...
(06Z TAFS)
Issued at 135 AM AST Thu Mar 12 2026

VFR conds will prevail across all TAF sites. VCSH possible at all
terminals during the period. However, SHRA could cause periods of
MVFR condt mainly by 12/17Z at TJSJ/TJBQ/TJPS. E-NE winds btwn
10-15 kt with gusts up to 20 kt and sea breeze variations aft
12/14Z.

&&

.MARINE...
Issued at 135 AM AST Thu Mar 12 2026

A weakening of the pressure gradient across the northeastern
Caribbean will result in lighter winds. Winds are expected to remain
gentle to moderate, with seas decreasing to between 3 and 5 feet,
resulting in improving marine conditions today and into the early
part of the weekend. However, winds are forecast to begin increasing
again around Saturday night into Sunday, leading to rough and choppy
seas and likely prompting Small Craft Advisory conditions from late
in the weekend into early next week, with seas building to around 6
to 8 feet.

&&

.BEACH FORECAST...
Issued at 135 AM AST Thu Mar 12 2026

Today, winds are expected to subside, resulting in improved
conditions. However, the rip current risk will remain moderate along
north- and east-facing beaches of Puerto Rico, Culebra, and St.
Croix, and low elsewhere. The same pattern will continue through
early Sunday.

The risk is forecast to increase to high around Sunday night into
early next week, 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 135 AM AST Thu Mar 12 2026

The risk for fire weather treats remains LOW today, as winds are
expected to become light to moderate and RH values are expected
increase due to the arrival of another patch of moisture across
the area. At this time an RFD will not be issued, but we
encourage partners to continue monitoring conditions in the coming
days.

&&

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

$$

SHORT TERM/AVIATION/FIRE WEATHER...MMC
LONG TERM...MRR
MARINE/BEACH FORECAST...CVB/MMC

NWS SJU Office Area Forecast Discussion