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825
FXCA62 TJSJ 071817
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
217 PM AST Wed Oct 7 2026

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

.KEY MESSAGES...
Issued at 215 PM AST Wed Oct 7 2026

- Shower and thunderstorm activity associated to the tropical
  wave passing south of the islands is expected to continue this
  afternoon and on Thursday, with a limited to elevated flood risk
  over most of Puerto Rico and the USVI.

- An elevated heat risk is anticipated for Thursday, as hot and
  humid conditions are forecasted due to the lingering moisture
  from the departing tropical wave.

- A moderate risk of rip currents will persist through Thursday
  across north- and east-facing beaches of the islands.

&&

.Short Term(This evening through Friday)...
Issued at 215 PM AST Wed Oct 7 2026

A variable weather pattern was observed during the morning hours,
with mid- to upper-level cloudiness associated with a vigorous
tropical wave located about 200 miles south of Ponce over Caribbean
waters. Doppler radar detected a few showers moving northeastward
into Vieques around 8 AM, but rainfall accumulations were minimal.
An area of cloudiness and thunderstorms moved across southeastern
Puerto Rico, then northeastward across the east-central interior and
north-central sections. Associated rainfall resulted in water
ponding in some urban areas across east-central Puerto Rico. During
the afternoon, moderate to heavy showers spread across much of the
island. Radar-estimated rainfall accumulations ranged from 1 to 2
inches, with the heaviest rainfall occurring across east-central
sections. Maximum temperatures varied depending on cloud cover,
reaching the upper 80s across coastal and urban areas and the mid-
to upper 70s across mountainous regions. Heat indices ranged from
100 to 108F.

For the rest of the afternoon and into the evening hours, the
moisture field associated with the tropical wave will remain in the
area as the axis of the wave moves farther out of the region.
Therefore, light to moderate showers are expected along the windward
sections of the islands, with stronger showers over Caribbean waters
and the Mona Passage. On Thursday, the main weather feature at the
surface will be building high pressure over the Central Atlantic,
resulting in an east-southeasterly wind flow across the forecast
area. Although precipitable water values across the region will
maintain enough moisture for a moderate to high chance of rain, a
mid-level ridge dominating at 500 mb will suppress shower
development. As a result, the forecast calls for a variable morning
with afternoon convection along the northwestern sections of Puerto
Rico, where a limited flooding threat exists. On Friday, a similar
weather pattern will persist in the mid to upper levels, bringing
mostly stable weather, warmer temperatures at 500 mb, and a drier
air mass aloft. Consequently, weather conditions will remain
favorable, with less shower activity forecast for the islands.

Regarding the heat threat, the absence of morning cloudiness
tomorrow will allow for longer periods of sunshine, leading to
warmer temperatures and heat indices between 100 and 112F. As a
result, there is a limited to elevated heat risk across the islands.
Similar conditions are expected on Friday.

&&

.Long Term(Saturday through next Tuesday)...
Issued at 200 AM AST Wed Oct 7 2026

Latest global model guidance indicates a highly unstable pattern
unfolding across the northeastern Caribbean as we move through the
weekend and into early next week. While Saturday begins with
recovering moisture supporting seasonable weather conditions, a
potent upper-level cut-off low is forecast to dig southward from the
central Atlantic and stall over the local islands through the first
part of the week. As this feature settles over the region, mid-level
temperatures at 500 mb will drop from around -5 degrees Celsius on
Saturday down to -7/8 degrees Celsius between Monday and Wednesday.
This anomalous cooling aloft will produce steep mid-level lapse
rates and generally unstable conditions. Additionally, a favorable
250 mb jet will provide strong upper-level divergence and excellent
ventilation that can support deep, organized convection.

Alongside these favorable upper-level dynamics, a deep plume of
tropical moisture will pool across the region. Precipitable water
values, which begin the period around 1.80 inches, are projected to
climb and remain near or above 2.00 inches from Sunday through
Wednesday. The combination of this deeply saturated atmospheric
column with deep instability and strong upper-level lift can produce
multiple rounds of heavy showers and intense thunderstorms.
Consequently, there will be an elevated threat of urban and small-
stream flooding, localized flash flooding, strong gusty winds, and
frequent lightning strikes. While daytime heating and local effects
will still focus the most intense, slow-moving convection over the
interior and western portions of Puerto Rico, the broad synoptic
forcing will also bring periods of locally heavy rainfall and strong
thunderstorms to the USVI and eastern PR.

&&

.AVIATION...
(18Z TAFS)
Issued at 215 PM AST Wed Oct 7 2026

Aftn SHRA/TSRA associated with a passing tropical wave will continue
to develop and spread across portions of southern PR, and from the
interior to W-NW PR thru 07/23Z. Brief MVFR/IFR conds are possible
in heavier SHRA/TSRA, along with mtn obsc, particularly at
TJBQ/TJPS. Additional SHRA will result in VCSH/-SHRA at
TJSJ/TIST/TISX thru 07/22Z. Locally reduced VSBY, LTG, lower CIGs
and gusty/VRB winds possible. ESE winds 10-15 kt thru 07/23Z,
becoming light/VRB overnight.

&&

.MARINE...
Issued at 215 PM AST Wed Oct 7 2026

The interaction between the high-pressure system and the tropical
wave passing south of the islands is tightening the pressure
gradient, promoting moderate to locally fresh winds. This will
induce choppy conditions primarily across Caribbean waters and local
passages. The wave will also bring increased shower and thunderstorm
activity, where the strongest storms could be accompanied by locally
strong gusty winds and higher seas leading to locally hazardous
marine conditions. As the wave departs tonight into Thursday, the
high-pressure system will linger north of the islands, maintaining
mainly gentle to moderate easterly trade winds.

&&

.BEACH FORECAST...
Issued at 215 PM AST Wed Oct 7 2026

A small northerly swell and a tropical wave moving across the area
will maintain a moderate risk of rip currents today along the north-
, east- and south-facing beaches of Puerto Rico, as well as Vieques,
Culebra, and the U.S. Virgin Islands. The moderate risk continues
tomorrow for north- and east- facing beaches, including most beaches
in the USVI.

Shower and thunderstorm activity associated to the tropical wave
could increase this afternoon and overnight, enhancing the lightning
risk at most beaches. Locally gusty winds are also possible near
thunderstorms.

&&

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

$$

SHORT TERM...LIS
LONG TERM....KML
AVIATION...GRS
KEY MESSAGES/MARINE/BEACH FORECAST...MNG/JCP

NWS SJU Office Area Forecast Discussion