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435
FXCA62 TJSJ 050853
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
453 AM AST Tue May 5 2026

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

.KEY MESSAGES...
Updated at 450 AM AST Tue May 5 2026

* A modest increase in moisture combined with an approaching trough
  will bring a higher chance of isolated to scattered showers this
  afternoon. Isolated thunderstorms cannot be ruled out.

* Mostly fair weather will prevail for the rest of the period, with
  passing trade wind moisture bringing isolated showers, mainly
  during overnight and morning hours.

* Above-normal temperatures will persist, promoting elevated heat
  indices across urban and coastal areas.

* Moderate rip current risk will continue along north- and east-
  facing beaches of the islands at times.

&&

.Short Term(Today through Thursday)...
Issued at 450 AM AST Tue May 5 2026

During the overnight hours, weather conditions remained fairly
tranquil across Puerto Rico and the U.S. Virgin Islands, with mostly
clear to partly cloudy skies and only a few very isolated showers
observed over the surrounding waters.

For the morning hours, a slight uptick in passing showers is
expected across windward coastal areas as a patch of moisture moves
over the region, as indicated by GOES-19 imagery. Precipitable water
(PWAT) values are forecast to increase to around 1.8 inches, which
is near normal for this time of year. This moisture increase will
also allow 700-500 mb relative humidity values to recover closer to
climatological levels, potentially weakening the trade wind
inversion that was more persistent yesterday.

From a dynamical perspective, instability aloft is expected to
increase as an upper-level trough approaches from the west. This
feature will promote a noticeable drop in 250 mb height fields and
support mid-level cooling, with 500 mb temperatures decreasing to
below-normal values. As a result, 700-500 mb lapse rates are
expected to steepen to above-normal values, while low-level lapse
rates remain comparatively weaker. This vertical pattern suggests
that any deep convection developing this afternoon will still rely
heavily on sea breeze convergence and local effects. The combination
of slightly higher moisture content, a temporarily weakened
inversion cap, and above-normal low-level temperatures driven by
persistent southeasterly flow could provide sufficient support for
isolated convective activity. However, the overall moisture increase
remains modest, and some mid-level drying is still present, which
will act as a limiting factor for widespread or sustained convection.

Therefore, afternoon activity is expected to remain localized,
particularly across the northwestern quadrant of Puerto Rico.
Streamer development downwind of the U.S. Virgin Islands and El
Yunque, moving northwestward, is also likely. At most, a limited and
very localized flooding risk is anticipated, with the potential for
a few isolated thunderstorms. For the remainder of the short-term
period, although some degree of dynamical instability aloft may
persist, especially into Wednesday, the primary limiting factor
will continue to be moisture availability. Wednesday afternoon
could feature a similar pattern to today, though outcomes will
depend on the timing and extent of drier air intrusions, which may
re-establish inversion caps and suppress convection. By Thursday,
conditions are expected to become more stable, resulting in the
least active day of the period.

Overall, mostly fair weather conditions will prevail, but patches of
moisture embedded in the southeasterly trades will modulate shower
activity. These will bring isolated overnight and morning showers
across windward areas at times, followed by localized afternoon
convection, mainly over interior and northwestern Puerto Rico.
Tuesday presents the highest chance for isolated thunderstorms,
though activity will remain limited with minimal flooding risk.

&&

.Long Term(Friday through Tuesday)...
Issued at 450 AM AST Tue May 5 2026

East to east-northeast flow to start the period will steer patches
of both drier and more humid air towards the region. Precipitable
Water (PWAT) values will generally be at below normal to low end
normal values for this time of the year. Available moisture will
also be shallow, mainly below 800 mb. With this below normal to
normal moisture and increasing subsidence (an upper level trough
will be moving away from the region to start the period and mid-
level ridging will build) a general reduction in shower activity and
rainfall coverage is forecast. A limited heat risk is also forecast
for most of the period, affecting sensitive individuals and
individuals with prolonged exposure and/or inadequate hydration.
Current model guidance suggests a more easterly steering flow to
start the next week, veering to become more easterly to east-
southeasterly to start the next workweek and continuing to bring
patches of both drier and more humid air. Up to breezy conditions
will be present, particularly to start the weekend onwards.

This will result in a limited non-thundersstorm wind risk, with
gusts up to around 25 mph at times at coastal and windward areas.
Unsecured items could blow around. Shower activity can continue to
reach windward sectors of the islands during the morning and
overnight hours while diurnal heating and local effects can
promote afternoon convection over mainly interior to western PR
with steering flow each day determining a more NW or SW movement.
Low concentrations of Saharan Dust will reach the area while the
bulk of a Saharan Air Layer will stay south of the local islands.
Under breezy conditions, increasing temperatures and with patches
of drier air approaching, the potential for elevated fire danger
remains, stay tuned for any future updates.

&&

.AVIATION...
(06Z TAFS)
Issued at 450 AM AST Tue May 5 2026

Mainly VFR conds expected to prevail across all terminals. However,
VCSH possible aft 05/16Z across most sites, with brief SHRA mainly
impacting TJBQ/TJSJ. A PROB30 group is in place for TJBQ btwn 17-21Z
for TSRA with brief MVFR conds possible. Winds will E-SE 10-15 kt
aft 13Z with occasional higher gusts and sea breeze variations.

&&

.MARINE...
Issued at 450 AM AST Tue May 5 2026

Broad surface highs and frontal boundaries over the Atlantic will
maintain an easterly to southeasterly flow through at least early
Thursday, backing to become more east to northeast through at least
Saturday. Up to moderate winds will continue, with periods of
locally fresh winds across the offshore waters and passages at
times. Seas will range between 2 and 4 feet, occasionally higher due
to a combination of local wind waves and a few pulses of a small,
long-period northeasterly swell spreading across the Atlantic
waters. Generally favorable conditions for small craft, though
operators should exercise caution at times due to wind-driven seas
and passing showers that may produce locally higher winds and
seas.

&&

.BEACH FORECAST...
Issued at 450 AM AST Tue May 5 2026

Up to a moderate risk of rip currents (life-threatening rip currents
are possible in the surf zone) will continue today for the north and
east beaches of Puerto Rico, as well as exposed beaches of Culebra
and St Croix. Pulses of small, long-period northeasterly swells will
continue to occasionally promote higher breakers and stronger rip
currents. A low risk of rip currents will continue elsewhere.
However, even if the risk for rip currents is low, life-threatening
rip currents often occur in the vicinity of groins, jetties, reefs,
and piers. A similar pattern will continue at least through at least
early Thursday. There is a chance of the low risk of rip currents
dominating on Friday, however the moderate risk will return Saturday
and spread to most beaches Sunday. For additional information,
visit: weather.gov/beach/sju.

&&

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

$$

SHORT TERM/AVIATION...CVB
LONG TERM/MARINE/BEACH...MRR

NWS SJU Office Area Forecast Discussion