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070
FXCA62 TJSJ 011902
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
302 PM AST Tue Sep 1 2026

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

.KEY MESSAGES...
Issued at 258 PM AST Tue Sep 1 2026

* Afternoon showers and thunderstorms will result in periods of
  moderate to heavy rain, which could cause ponding and localized
  flooding in urban areas and small streams, especially across
  Puerto Rico`s western half. The US Virgin Islands will see
  passing showers.

* Moderate Rip Current Risk: Life-threatening rip currents will
  be possible along the north and east remain likely along north-
  and east- facing beaches of Puerto Rico and the U.S. Virgin
  Islands through this evening.

* Increasing Heat: Abundant moisture combined with hot
  temperatures will result in an elevated to high risk of extreme
  heat, particularly tomorrow, Wednesday.

* Beneficial rainfall ahead: Another tropical wave will increase
  rainfall chances by the end of the workweek. Additional moisture
  early next week could bring further beneficial rainfall to the
  region.

&&

.Short Term(This evening through Thursday)...
Issued at 258 PM AST Tue Sep 1 2026

Mostly calm weather prevailed in the morning, with maximum
temperatures in the upper 80s and low 90s and variable cloudy
skies, as we observed mostly cloudy skies across portions of the
USVI and eastern and western PR in the morning, with clear skies
along the interior and southern portions of PR. Later in the day,
a line of showers developed downwind from St Croix, affecting the
western parts and surrounding waters. Winds were mainly from the
east to east-southeast at 5 to 15 mph with sea breeze variations.

An upper-level trough will continue to increase local instability
across the northeast Caribbean. In addition, plenty of tropical
moisture will continue across the region through at least
Thursday. These features will continue to produce periods of heavy
showers and isolated strong thunderstorms each afternoon and
evening. Then, low-level convergence, enhanced by east- southeast
winds and local topography, will promote periods of showers across
the windward locations of the USVI and PR each day. This weather
pattern will continue to result in a limited to elevated risk of
flooding this afternoon and Wednesday.

Above-normal temperatures will continue across the region. As a
result, heat products associated with extreme heat may be needed
for Wednesday afternoon, especially in areas without rain.

Thursday, the driest day of the short-term forecast (at this
moment), will feature warm to hot temperatures with little or no
rain. This rain will mainly come from patches of moisture embedded
in the winds affecting the windward locations, followed by
afternoon convection across western PR and downwind from the USVI.

&&

.Long Term(Friday through Tuesday)...
Issued at 434 AM AST Tue Sep 1 2026

A surface high pressure extending from the central Atlantic into the
western Atlantic and two tropical waves will be the main weather
features during the long-term period. From Friday into Saturday, the
surface high pressure will maintain generally moderate easterly
winds across the region. Aloft, an upper-level low will remain
nearby, resulting in periods of upper-level cloudiness, while a mid-
level ridge near 500 mb should provide some stability. This stable
pattern is also reflected in the relatively warm 500-mb
temperatures, forecast to remain near -4C. These conditions should
limit widespread shower development; however, the available moisture
combined with local effects may enhance some afternoon convection
across western Puerto Rico, particularly in the vicinity of
Mayaguez. No significant rainfall threat is anticipated with this
activity. The main concern will continue to be excessive heat,
with warm temperatures and heat indices potentially reaching
around 111F. This is also supported by 925-mb temperatures
forecast to remain around two standard deviations above normal.
These conditions will support above-normal temperatures and
maintain the potential for elevated heat indices across Puerto
Rico and the U.S. Virgin Islands, where Heat Advisories may be
required. By late Friday into Saturday, precipitable water values
are expected to increase as a weak tropical wave moves across the
islands, with PWAT values rising to around 1.8 inches. This
feature will provide additional moisture for passing showers,
although the overall influence of the mid-level ridge should limit
widespread organized convection. Meanwhile, southerly winds
around 250 mb will begin to develop as the upper- level pattern
gradually evolves.

Conditions are expected to become more unsettled from Sunday into
Monday as a better-defined tropical wave, accompanied by deeper mid-
level moisture, moves across the region, resulting in a more
favorable environment for shower and thunderstorm development. Based
on the latest guidance, the deepest moisture associated with this
feature appears more likely to be displaced toward northern Puerto
Rico and the Atlantic waters. Additionally, southeasterly flow at
250 mb, combined with an area of positive cyclonic vorticity around
850 mb, should provide additional dynamical support, particularly
where the deeper moisture associated with the wave is present.
Therefore, an increase in shower and thunderstorm activity can be
expected during this period, with afternoon convection likely
becoming more active across portions of Puerto Rico. By Tuesday,
conditions should gradually begin to improve as the central Atlantic
surface high strengthens and the low-level winds become more
southeasterly across the local area. This evolving wind pattern
should gradually push much of the available moisture northward into
the Atlantic, allowing somewhat drier conditions to filter into the
region.

&&

.AVIATION...
(18Z TAFS)
Issued at 258 PM AST Tue Sep 1 2026

Mainly VFR conditions will prevail. However, VCTS/-TSRA will
continue to affect mainly TJSJ/TJBQ/TJPS thru around 01/21Z,
prompting brief to Tempo MVFR conditions. -SHRA/Iso -TSRA will
remain psbl for eastern and southern terminals thru much of the prd
as E-ESE flow continues to steer them towards the region. E-ESE flow
up to around 15 kt, with higher gusts and higher near TS, thru
01/23Z, decreasing overnight and picking up again from the E-ESE
after 02/12Z with sea breeze variations and local effects. VCTS/-
TSRA once again forecast at around 02/17Z and mainly affecting PR
terminals.

&&

.MARINE...
Issued at 258 PM AST Tue Sep 1 2026

A surface high pressure will continue to build over the far
eastern Atlantic and promote moderate trades through the workweek.
The next tropical waves are forecast to reach the local waters
toward the end of the workweek and early next week, bringing
another increase in shower and thunderstorm activity. For the rest
of today and this evening, lingering tropical moisture and a weak
trough will continue to promote shower and thunderstorm activity
across the regional waters.

&&

.BEACH FORECAST...
Issued at 258 PM AST Tue Sep 1 2026

A moderate risk of life-threatening rip currents will persist
along north- and east-facing beaches of Puerto Rico and the U.S.
Virgin Islands through this evening. Then, the moderate risk will
be limited to the northwest and northcentral portion of PR.

The risk will turn low through at least next week. However, we
encourage beachgoers to exercise caution as life-threatening rip
currents may still occur, especially near groins, jetties, reefs,
and piers. Always swim near a lifeguard and remember to heed the
advice of the local beach patrol and flag warning systems.

Thunderstorms are also expected across the region. If you hear
thunder, seek safe shelter immediately and stay away from the
beach and open water.

&&

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

$$

KEY MESSAGES/SHORT TERM/MARINE/BEACH FORECAST...CAM
LONG TERM....LIS
AVIATION...MRR

NWS SJU Office Area Forecast Discussion