652
FXCA62 TJSJ 211812
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
212 PM AST Thu May 21 2026

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

.KEY MESSAGES...
Issued at 208 PM AST Thu May 21 2026

* Morning showers across windward areas of PR and the USVI will be
  followed by afternoon showers and isolated thunderstorms,
  particularly across western PR.

* Breezy to locally windy conditions will continue across the local
  islands over the next several days. Secure loose objects.

* Moderate to locally strong winds will result in choppy to rough
  seas at times and a moderate rip current risk across most local
  beaches.

* Warm temperatures will persist each day, with heat indices
  remaining in the upper 90s to low 100s. This will primarily
  affect heat-sensitive individuals, especially those outdoors
  without adequate cooling or hydration.

&&

.Short Term(This evening through Saturday)...
Issued at 208 PM AST Thu May 21 2026

Most of the morning featured partly cloudy skies with quick-moving
showers across windward areas of Puerto Rico. Breezy to windy
conditions were observed at local weather stations, with easterly to
southeasterly winds of 10 to 20 mph and gusts reaching the upper 20s
to lower 30s mph. Daytime highs ranged from the upper 80s to lower
90s across urban and coastal areas and from the upper 70s to lower
80s across higher elevations. Heat indices reached the mid 90s to
around 100 to 102 degrees F.

Current weather conditions across Puerto Rico and the U.S. Virgin
Islands are being influenced by a weakening mid to upper-level
trough, while a weak mid-level ridge will start building over the
region. At the surface, a strengthening high-pressure over the
central Atlantic is tightening the local pressure gradient,
promoting moderate to fresh, and at times locally strong, east to
southeasterly winds. This pattern is expected to persist through the
short-term period, unsecured items could blow around.

In terms of moisture, drier air has temporarily filtered into the
region today, lowering precipitable water (PWAT) values to around
1.3 to 1.4 inches. Supporting this trend, the 12Z sounding measured
a PWAT value of 1.44 inches, which is below normal for this time of
year. However, moisture levels are expected to gradually increase
through the remainder of the short term period, generally
fluctuating between 1.5 and 1.8 inches, near seasonal averages.

This afternoon, daytime heating and local effects will support
isolated to scattered showers across northwestern Puerto Rico. A
similar pattern is expected Friday and Saturday, although slightly
higher moisture levels may lead to a modest increase in morning
showers and somewhat stronger afternoon convection. Even so, breezy
conditions should keep showers moving quickly, limiting the
potential for significant flooding. Overall, this pattern remains
typical for the season, with morning trade wind showers followed by
afternoon convection over western Puerto Rico.

Warm temperatures will also persist, particularly across coastal and
urban areas. Based on climatology and guidance for 925 mb
temperatures, values should remain near seasonal normals for late
May. Expect daytime highs to continue in the upper 80s to low 90s
across lower elevations of Puerto Rico and the USVI, while higher
elevations remain in the upper 70s to mid 80s. Heat indices could
rise into the upper 90s to low 100s degrees F.

&&

.Long Term(Sunday through next Wednesday)...
Issued at 208 PM AST Thu May 21 2026

Small changes were introduced to the long-term forecast, as variable
conditions may persist early next week, becoming wetter by the end
of the period. The wind pattern will continue from the E-ESE as a
surface high pressure building in the western Atlantic, maintaining
breezy to windy conditions from Sunday through Tuesday, peaking on
Monday. However, the high pressure may migrate eastward and linger
over the Central Atlantic, weakening and veering winds from the SE
Tuesday onward. Moisture content should remain seasonal, with PWAT
values ranging between 1.5 and 1.75 inches on Sunday and Monday, but
it should gradually increase as abundant moisture pools into the
region. According to the latest model guidance, PWAT values could
increase up to 2.0 inches, near the climatological normal, with low
and mid-level moisture increasing well above normal and sounding
models showing skinny profiles. Due to the proximity of the upper-
level trough, mid-level temperatures should briefly cool both Sunday
and Monday (around -8 degrees Celsius), gradually warming as a mid-
level ridge north of the CWA weakens the trough. Although shower
activity is expected each day of the forecast, for Sunday and
Monday, fast-moving showers are expected over half of eastern Puerto
Rico and the U.S. Virgin Islands, with afternoon convection over
interior and western Puerto Rico. Additionally, streamers should
develop by midday, moving over portions of Vieques, Culebra, and
eastern Puerto Rico, including the San Juan Metropolitan Area.
Rainfall accumulations could result in ponding of water over
roadways and poorly drained areas, along with minor flooding, with a
limited flooding threat. Besides flooding, these areas can
experience gusty winds and lightning. As winds shift and moisture
content increases, the flood threat may remain limited, but an
elevated threat (including urban and small stream flooding) over
localized areas cannot be ruled out.

With abundant moisture and seasonal temperatures across the region,
heat indices over localized areas (particularly urban and coastal)
of the islands may reach and exceed 100 degrees Fahrenheit.
Nevertheless, the heat will remain limited, likely to impact those
sensitive to heat. Stay hydrated and avoid long sun exposure.

&&

.AVIATION...
(18Z TAFS)
Issued at 208 PM AST Thu May 21 2026

VFR conditions will prevail across all TAF sites during the
period. Breezy conditions will persist, with winds up to 18 knots
and gusts up to 25 knots from the E. Winds will diminish at
21/23Z, becoming from the E up to 10 knots. Brief MVFR conditions
are possible across TJBQ & TJSJ due to localized SHRA to TS
reducing VIS and lowering ceilings, affecting FL020 to FL050.
Across mountains, lower ceilings are forecast as well due to SHRA.
VCSH is expected along the east side from 21/23Z to 22/06Z.

&&

.MARINE...
Issued at 208 PM AST Thu May 21 2026

A broad surface high pressure over the Central Atlantic, combined
with a long stationary frontal boundary stall across the central
Atlantic, will continue to result in a pressure gradient tight,
increasing the surface winds, and steadying moderate to locally
fresh winds from the east. This will result in some wind-driven
seas across the offshore Atlantic waters, where a Small Craft
Advisory is in effect until 6 PM AST this evening. Mariners are
urged to remain aware of the marine conditions in that area. For
the rest of the period, windy conditions will persist, resulting
in similar conditions across the local exposed areas and some very
exposed coastal areas.

An increase in moisture and cloudiness by the upcoming weekend
might enhance shower activity along the marine areas, resulting in
thunderstorm activity that could result in localized hazardous
marine conditions. Please stay aware of weather conditions before
heading to sea.


&&

.BEACH FORECAST...
Issued at 208 PM AST Thu May 21 2026

The forecast remains on track. A moderate risk of rip currents
will continue across most local beaches through the next several
days due to persistent breezy conditions and ongoing wind-driven
seas. The highest risk will persist along north- and east-facing
beaches of Puerto Rico, Culebra, and the U.S. Virgin Islands.
Beachgoers should exercise caution, as life-threatening rip
currents remain possible.

&&

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

&&

$$

SHORT TERM, KEY MESSAGES...YZR
LONG TERM....MNG
AVIATION, MARINE & BEACH FORECAST...LIS

NWS SJU Office Area Forecast Discussion