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358
FXCA62 TJSJ 070754 CCA
AFDSJU

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
354 AM AST Wed Oct 7 2026

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

.KEY MESSAGES...
Issued at 200 AM AST Wed Oct 7 2026

- Increasing moisture associated with a nearby tropical wave will promote
  a wetter and more active weather pattern today. As a result,
  there is an increased chance of periods of heavy rainfall and
  thunderstorms. A limited to elevated flood risk will persist
  across the islands today.

- On Thursday, lingering moisture and southeast flow will likely support
  hot and humid conditions, along with afternoon showers and
  thunderstorms across interior and western areas of Puerto Rico.

- A more seasonal weather pattern is expected to return by the end of
  the week. From Sunday into early next week, models suggest that
  a more unstable atmosphere may return. Stay tuned to the
  forecast.

- A moderate risk of rip currents is expected through Thursday
  night mainly along portions of the north- to southeast-facing
  beaches of the islands, then a low risk is forecast for Friday
  and continuing through the weekend.

&&

.Short Term(Today through Friday)...
Issued at 200 AM AST Wed Oct 7 2026

The overnight hours kicked off the short term period with an active
period of weather. The humidity associated to a tropical wave
filtered its way into the region bringing above average precipitable
(PWAT) values to the US Virgin Islands and eastern Puerto Rico. This
lead to the development of showers across the offshore waters, US
Virgin Islands and the eastern half of Puerto Rico. While
significant accumulations have not been registered by the radar, the
activity will continue throughout the day. Where recurring rainfall
and downpours occur the flooding risk will be moderate. This means
that flooding in urban areas, roads, small streams and washes, as
well as low chance for isolated flash floods is possible. Convection
has already induced wind gusts up to 30 mph in portions of the US
Virgin Islands and southern Puerto Rico.

The rest of today should be dominated by a variable weather pattern
associated to the wave passage over the islands. While a couple of
mid-level high pressure systems to the north of the CWA are acting
to limit the development of deep convective cells by warming the
layer and weakening the lapse rates at these levels, the wave will
provide sufficient instability for the development of widespread
showers and localized thunderstorms. Model guidance indicates
increased values of PWAT and column RH which will further aid in the
development of convective activity. A surface high pressure system
to the north of the region is currently promoting breezy ESE
conditions which will further act to advect warm and moist air from
the wave into the region. The winds will gradually reduce into the
afternoon which will allow convection to linger which may aid in the
development of flooding wherever persistent recurring rainfall
occurs. Given the amount of widespread cloud coverage expected for
the day the heat risk remains limited. Individuals are invited to
remain informed of the evolving weather conditions and forecasts as
they become available.

Similar favorable features will be present on Thursday. Lingering
moisture from the wave should provide sufficient instability for the
development of showers and thunderstorms. The focus of the activity
for this day will be on the northwest portion of Puerto Rico where a
moist vertical column will prevail. Nonetheless, breezy ESE
conditions will return aiding in the development of streamers from
el Yunque and the smaller islands, which will predominantly affect
the US Virgin Islands and eastern Puerto Rico during the afternoon,
and advective showers over the night and morning. Given that
convection for the day will be more localized and have less cloud
coverage and with 925 mb temperatures 2 standard deviations above
average for the season, the heat risk for Thursday is elevated. This
level of heat can affect most individuals sensitive to heat,
especially those without effective cooling and adequate hydration.
We recommend limiting outdoor activities and staying hydrated.

By Friday a mass of drier air will filter into the region promoting
predominantly fair weather. The column will also be dominated by
drier mid-to-upper levels further inhibiting the development of
convection. The mid-level high pressure systems will continue
enhancing warming and weakening of the lapse rates at these levels.
This will act to cap convection and limit the development of deep
convection. With the low-level high pressure system moving
further north the steering flow is expected to shift to be from
the ENE bringing drier cooler air to the islands. The activity
that does develop will thus be driven by local effects and should
be focused on the western interior and southwestern region of
Puerto Rico. This breezy northeasterly windflow should also
provide some respite to the warm conditions across the islands,
hence a limited heat risk is expected for the day.

&&

.Long Term(Saturday through Wednesday)...
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...
(06Z TAFS)
Issued at 200 AM AST Wed Oct 7 2026

Mainly VFR conditions thru the forecast period, but intermittent
periods of MVFR/IFR conds will occur today as a tropical wave brings
the potential for SHRA/TSRA across most TAF sites. This morning
mainly across USVI and TJSJ/TJPS sites, then likely spreading into
TJBQ later today. Expect locally reduced VSBY, LTG, lower CIGS, and
gusty/VRB winds near stronger rain activity. ESE winds 10-15 kt with
some periods of higher gusts, then becoming light/VRB aft 07/23Z.
&&

.MARINE...
Issued at 200 AM AST Wed Oct 7 2026

Surface high pressure continues to move east across the central
Atlantic while a frontal boundary advances across the western
Atlantic, north of the local area. The interaction between the high
pressure and an incoming tropical wave will tighten the pressure
gradient through this morning, generating choppy conditions
primarily across Caribbean waters and local passages. The wave will
also bring increased shower and thunderstorm activity, accompanied
by locally strong gusty winds and higher seas. As the wave departs
late Wednesday into Thursday, another high-pressure system will move
across the western Atlantic, maintaining mainly gentle to moderate
easterly trade winds.

&&

.BEACH FORECAST...
Issued at 200 AM AST Wed Oct 7 2026

The combination of 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, as well as most of the USVI.

The tropical wave will increase shower and thunderstorm activity
through tomorrow, resulting in an increased 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...RVM
LONG TERM...DSR
AVIATION...YZR/DSR
MARINE/BEACH FORECAST...KML

NWS SJU Office Area Forecast Discussion