494
FXCA62 TJSJ 220716
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
316 AM AST Sat Aug 22 2026

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

.KEY MESSAGES...
Issued at 310 AM AST Sat Aug 22 2026

 * Hot and humid conditions will maintain an elevated heat threat
   across coastal and urban areas, with heat indices potentially
   reaching around 110F. A Heat Advisory is in effect for areas
   where the highest heat indices are expected from 10 AM to 5 PM
   AST today.

 * Variable weather conditions are expected today, with periods of
   passing showers alternating, followed by additional afternoon
   shower development due to daytime heating and local effects.

 * A weak tropical wave will approach and move across the region
   on Monday, increasing moisture and the frequency of showers, although
   the deepest moisture is expected to remain mainly south over
   the Caribbean waters.

 * A low to moderate risk of rip currents will continue across
   several local beaches for the upcoming days.

&&

.Short Term(Today through Monday)...
Issued at 310 AM AST Sat Aug 22 2026

Isolated to scattered showers were observed from late Friday into
the early morning hours on Saturday across most of the region. A
line of showers moved across the area from east to west, resulting
in variable weather conditions with generally minimal rainfall
accumulations. The strongest showers were detected by Doppler
radar just south of the coastal areas between Ponce and Juana
Diaz. Shower activity also moved westward, affecting several
northern coastal municipalities before gradually diminishing
around 2 AM. Overnight temperatures were in the lower 80s across
coastal areas and in the lower to mid-70s across the mountainous
sections. Winds were generally from the east-northeast at around
10 mph, with occasional gusts accompanying the showers.

East-northeasterly winds will remain in place through at least
the early morning hours today, gradually becoming more easterly
and allowing showers to affect eastern and northeastern Puerto
Rico. Sufficient moisture will continue to reach the islands as a
patch of moisture moves across the region, followed by another
area of moisture during the afternoon, with precipitable water
values ranging from 1.8 to 1.9 inches. These conditions will
support a showery pattern under breezy conditions, as a surface
high pressure system over the western Atlantic maintains a tight
pressure gradient across the region. Given the expected
conditions, showers will generally be fast-moving, keeping
rainfall accumulations on the lower side, particularly across
eastern Puerto Rico and the eastern interior. By the afternoon,
high-resolution models suggest an increase in shower activity
across northwestern and western interior Puerto Rico, mainly due
to diurnal heating and local effects. These factors could support
locally moderate to briefly heavy showers; however, the presence
of a mid-level ridge will inhibit more widespread and persistent
shower development.

 On Sunday, at the surface, a high-pressure system over the
Atlantic, in combination with an area of low pressure over the
central Atlantic, will promote a more east-southeasterly wind flow
across the region. According to the global model guidance, during
the morning hours, a relatively dry slot of air is expected to
filter into the local area, limiting the frequency and coverage of
shower activity. Therefore, generally fair weather conditions
should prevail for much of the morning, although a few brief
showers cannot be ruled out, especially across windward coastal
areas. Moisture is then expected to gradually increase from the
late morning into the afternoon, with precipitable water values
increasing. The combination of this increase in available
moisture, daytime heating, and local effects should support
afternoon shower development, mainly across portions of the
interior and western to northwestern Puerto Rico. Given the
expected steering flow, showers should generally move toward the
west-northwest. However, the overall environment is not expected
to be particularly unstable, which should limit the potential for
widespread or prolonged rainfall activity. By Monday, the low-
level wind flow is expected to become more easterly as a weak
tropical wave approaches and moves across the region. Moisture
will increase in association with the wave, resulting in a
slightly wetter pattern compared to Sunday. Although the bulk of
the tropical moisture is forecast to pass south of the islands and
remain primarily over the Caribbean waters, the northern portion
of the moisture field should extend across Puerto Rico and the
U.S. Virgin Islands. This should be sufficient to increase the
frequency of passing showers across eastern Puerto Rico and the
local waters during the morning hours.

In addition to the rainfall potential, heat will remain a concern
through Sunday and Monday, particularly across the coastal and
urban areas of Puerto Rico and the U.S. Virgin Islands. Warm
temperatures combined with elevated low-level moisture will result
in heat indices potentially reaching around 110F across some
coastal and urban locations. The highest heat indices are expected
during the late morning and early afternoon hours, before
afternoon shower activity provides some localized relief.
Therefore, residents should remain aware of the potential for
heat-related impacts, especially in areas where shower activity
remains limited.

&&

.Long Term(Tuesday through Saturday)...
Issued at 310 AM AST Sat Aug 22 2026

The main long-term forecast concerns are persistent excessive heat
and the evolution of the mid-level ridge as a couple of weak
tropical disturbances move through the Caribbean. Confidence remains
moderate through Tuesday, then decreases somewhat for the latter
half of the week as model differences become more pronounced.

On Monday, the deterministic GFS suggests the mid-level ridge will
erode by the afternoon. If this occurs, reduced mid-level inhibition
combined with daytime heating and local effects should support a
better opportunity for afternoon convection across the interior and
western portions of Puerto Rico. Farther east, the U.S. Virgin
Islands and windward portions of Puerto Rico should experience
mainly isolated, fast-moving showers. Limited to elevated excessive
heat conditions will remain a concern, particularly across coastal
and urban areas.

By Tuesday, a weak tropical wave is forecast to approach the region.
However, the deterministic GFS and ECMWF differ on the strength of
the mid-level ridge and associated moisture. Nevertheless,
increasing moisture should support showers and isolated
thunderstorms across the U.S. Virgin Islands and eastern Puerto Rico
as early as Tuesday morning, followed by additional convection over
the interior and western portions of Puerto Rico during the
afternoon. Confidence in rainfall coverage and amounts remains
limited, however. The GFS is more aggressive in weakening the mid-
level ridge, while guidance also suggests increasing trade winds. A
faster low-level flow could limit rainfall duration and reduce the
potential for significant accumulations.

Any rainfall would be beneficial given the ongoing drought
conditions across portions of Puerto Rico and the U.S. Virgin
Islands, particularly if precipitation occurs within reservoir
watersheds. However, given the expected progressive nature of the
showers and current model uncertainty, confidence remains low that
this wave will provide meaningful drought relief.

Guidance generally favors the mid-level ridge rebuilding over the
region Wednesday, which should once again suppress widespread
convection while maintaining hot conditions. Another disturbance is
being monitored for Thursday, although current GFS guidance keeps
the bulk of its moisture and associated activity south of the local
islands over the Caribbean Sea. Another possible tropical wave may
approach Friday, but current guidance suggests limited organization
and moisture. Given the lead time and model variability, confidence
in the Thursday-Friday evolution remains low.

Overall, periods of excessive heat will remain one of the primary
hazards during the long-term period, particularly Monday and Tuesday
and potentially into Wednesday. Rainfall opportunities will increase
at times with passing disturbances, but confidence in significant or
widespread accumulations remains low.&&

.AVIATION...
(06Z TAFS)
Issued at 310 AM AST Sat Aug 22 2026

VFR conds are expected to prevail across all local terminals
through the fcst period. E-ENE winds at 10-15 kt will prevail,
increasing to 15 kt aft 22/14Z. Passing SHRA will continue to
move across the local area, mainly affecting TJSJ/TIST/TISX during
the AM hrs. Brief -SHRA/SHRA may result in tempo reduced VIS and
lower CIGs at times. Aft 22/16Z, diurnal heating and local effects
will favor SHRA development across interior and W/NW PR.

&&

.MARINE...
Issued at 310 AM AST Sat Aug 22 2026

A surface high pressure over the Western Atlantic in combination
with a low pressure system across the central Atlantic will
allow moderate easterly winds across the region. This will favor
seas between 3-5 feet with occasionally seas up o 6 feet across
offshore Atlantic waters. Given the expected conditions, mariners
should stay tune for weather updates. Today some showers with
thunderstorms can result in localized hazardous marine conditions.


&&

.BEACH FORECAST...
Issued at 310 AM AST Sat Aug 22 2026

Expect risk to be low across most islands through at least Monday.
Regardless, life-threatening rip currents can occur near groins,
jetties, reefs, and piers. From Tuesday into midweek, winds are
expected to gradually become breezier, with a moderate risk
expanding to most local beaches.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ001>005-007-008-010>013.

VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for VIZ001-002.

AM...None.
&&

$$

SHORT TERM...LIS
LONG TERM....MMC
AVIATION...CAM