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754
FXCA62 TJSJ 021636
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1236 PM AST Wed Sep 2 2026

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

.KEY MESSAGES...
Issued at 1206 PM AST Wed Sep 2 2026

- Afternoon showers and thunderstorms will continue to affect the
  interior and western Puerto Rico. Ponding of water and localized
  flooding are possible in urban areas, on roads, and near small
  streams. Streamers will continue to develop from the islands.

- A Heat Advisory remains in effect for Puerto Rico and the U.S.
  Virgin Islands through 4 PM AST. Heat will remain one of the
  primary hazards in the coming days, particularly this next
  weekend.

- A low risk of rip currents will prevail over the coming days.
  However, even when the overall risk is low, life-threatening rip
  currents can occur near groins, jetties, reefs, and piers.

- A weak tropical wave will increase the chances of rain Friday
  into Saturday. Then, early next week, additional moisture could
  bring more rainfall chances to the region.

&&

.Short Term(This evening through Friday)...
Issued at 1206 PM AST Wed Sep 2 2026

A drier and more stable air mass will promote mostly calm weather
tonight through Thursday. Precipitable water and mid-level
moisture are expected to fall below normal, limiting shower
coverage and deeper convective development. A few brief trade
wind showers may still affect windward areas, mainly during the
nighttime and early morning hours, but significant rainfall
impacts are not expected through Thursday.

Weather conditions will begin to change Friday as a weak tropical
wave approaches the islands from the east. Moisture will
gradually increase during the day, with showers becoming more
frequent as the wave gets closer to the US Virgin Islands and
Puerto Rico. The highest potential for unsettled weather is
expected from Friday night into Saturday, when the deepest
moisture moves across the region. Although the wave is expected to
remain weak, periods of moderate to locally heavy rainfall and
isolated thunderstorms are possible. The main potential impacts
will be ponding of water on roads and localized flooding in low
lying and poor drainage areas, especially where showers persist or
repeatedly affect the same locations. Thunderstorms may also
produce lightning and brief gusty winds. Outdoor activities should
generally experience favorable conditions through Thursday. Those
with plans Friday night into Saturday should be prepared for
periods of showers and possible thunderstorms and remain alert for
localized flooding where heavier rainfall develops.

Temperatures will remain warm through the period, with daytime highs
generally near to slightly above normal. Coastal and urban areas
can expect highs in the upper 80s to lower 90s, while temperatures
across the interior should generally remain in the upper 70s to
lower 80s. The combination of warm temperatures and limited
rainfall may result in uncomfortable conditions during the
afternoon, particularly through Thursday. Residents and visitors
planning prolonged outdoor activities should stay hydrated and
take breaks from the heat, and continue to monitor the forecast
for any heat-related products that may be issued.

&&

.Long Term(Saturday through next Tuesday)...
Issued at 1206 PM AST Wed Sep 2 2026

A surface high pressure over the central Atlantic, a mid-level
ridge, and the passage of a tropical wave by Tuesday will be the
main weather features during the long-term period. On Saturday, the
surface high pressure over the central Atlantic will maintain a
southeasterly wind flow across the region. Moisture will remain
relatively high, with precipitable water values around 1.9 inches.
However, at the mid-levels, a ridge near 500 mb will promote warmer
temperatures and a strong trade wind cap, providing enough stability
to limit the vertical development of showers. At the upper levels,
southerly winds around 250 mb will continue to bring periods of
upper-level cloudiness across the region. Therefore, despite the
available moisture, generally stable conditions should limit
widespread rainfall activity. The main concern on Saturday will
continue to be the heat threat, particularly across coastal and
urban areas.

From Sunday into Monday, the surface pressure gradient will weaken
as the high pressure remains over the central Atlantic, resulting in
lighter winds across the islands. Winds are expected to become more
southerly to southeasterly at the lower levels, while southwesterly
winds prevail near 250 mb. Meanwhile, moisture will gradually
increase, with precipitable water values approaching 2.0 inches. The
combination of weak steering winds, abundant moisture, and local
effects should favor afternoon convection, particularly across the
interior and northern portions of Puerto Rico. Slow-moving showers
could result in locally higher rainfall accumulations, although
widespread activity is not anticipated at this time. By Tuesday,
weather conditions are expected to become more unstable as the
moisture field associated with a tropical wave moves across the
region. Model guidance suggests precipitable water values could
increase to around the 75th percentile for this time of year,
indicating an anomalously moist environment. In addition, an upper-
level low is forecast to become positioned near the region,
increasing instability aloft and providing better upper-level
support for convective development. Upper-level disturbances
generally favor enhanced clouds and precipitation by increasing
instability and lift. Therefore, Tuesday currently appears to have
the greatest potential for more widespread shower and thunderstorm
activity, along with an increasing potential for locally heavy
rainfall.

&&

.AVIATION...
(18Z TAFS)
Issued at 1206 PM AST Wed Sep 2 2026

Brief periods of MVFR conds will remain possible in and
around JSJ/JPS and JBQ in SHRA/TSRA through about 02/20z.
Afterwards, VFR conds expected at all TAF sites. Easterly winds at
10kt with sea breeze variations, becoming light and variable
overnight.

&&

.MARINE...
Issued at 1206 PM AST Wed Sep 2 2026

A surface high pressure will continue to build over the far eastern
Atlantic and promote gentle to moderate trades through the workweek,
with seas between 2 and 4 feet, occasionally 5 feet. The next
tropical waves are forecast to reach the local waters and passages by
Friday into the weekend, increasing shower and thunderstorm activity
and bringing gusty winds and lightning.

&&

.BEACH FORECAST...
Issued at 1206 PM AST Wed Sep 2 2026

A low risk of rip current is expected to continue throughout the
week, likely to become moderate early next week. Aside from rip
currents, beachgoers should stay weather alert, particularly each
afternoon, due to shower and thunderstorm activity that may move
near the western and northern coastal areas of Puerto Rico,
producing gusty winds and lightning. Beachgoers must seek shelter
whenever they hear thunder.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 4 PM AST this afternoon for PRZ001>013.

VI...Heat Advisory until 4 PM AST this afternoon for VIZ001-002.

AM...None.
&&

$$

SHORT TERM...MMC/JCP/RVM
LONG TERM...MNG
AVIATION...OMS

NWS SJU Office Area Forecast Discussion