222
FXCA62 TJSJ 010921
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
521 AM AST Sat Nov 1 2025

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

.KEY MESSAGES...
Issued at 457 AM AST Sat Nov 1 2025

* A tropical wave moving across the region today will lead to
  heavy showers and thunderstorms. This will result in an elevated
  flooding risk across portions of eastern, central and western
  Puerto Rico. Frequent lightning and gusty wind conditions can
  be expected with the strongest thunderstorms.

* Across the U.S. Virgin Islands, intermittent period of heavy
  showers and possible thunderstorms are expected today, resulting
  in a limited flood threat. The rest of the weekend expect
  passing showers at times.

* A moderate risk of rip currents is expected through the weekend
  at most beaches across Puerto Rico and the U.S. Virgin Islands.
  Additionally, a Small Craft Advisory for the offshore Atlantic
  waters is in effect from this evening through Sunday morning.

&&

.SHORT TERM (Today through Monday)...
Issued at 457 AM AST Sat Nov 1 2025

Since midnight, radar estimated accumulations show at least minimal
accumulations over the U.S. Virgin Islands, Vieques, Culebra and
over eastern, southeastern, central and southwestern Puerto Rico.
Lows have been in the mid 70s to the low 80s at lower elevations of
Puerto Rico and from the mid 60s to low 70s at higher elevations of
Puerto Rico. Lows have been in the upper 70s to low 80s at the USVI.

Current satellite derived precipitable water (PWAT) imagery indicate
an airmass with values above 2 inches over our area in relation to
an approaching tropical wave. Although this wave will move mainly
south of the islands, deep tropical moisture, cloudiness, showers
and t-storms will continue to be steered towards the islands from
the Caribbean Waters today, promoting a more variable to showery
pattern. An upper low southwest of Puerto Rico will continue moving
westward and away from the local region to start the period. Today,
PWAT values can reach up to 2.50 inches with 500 mb temperatures
starting at around -6C to start the period and then gradually
increasing to around -2C before decreasing again. Conditions today
will be favorable for shower and t-storm development over the
waters, moving into windward sectors of the islands. Development of
showers and t-storms continues to be forecast for interior to
western PR later today as well. This will all promote a limited to
elevated flooding risk for the region today along with a limited
lightning risk. Steering flow in general will continue from the ESE
through most of the rest of the weekend as a high pressure system
over the central Atlantic gradually moves northward. Steering flow
is forecast to become more easterly late Sunday and Monday.

925 mb wind speeds are forecast at high end normal to slightly above
normal values, resulting in up to breezy conditions for the period.
Notable changes are expected to start next week, tomorrow. By early
tomorrow, Sunday, drier air will filter in as a ridge establishes
itself, limiting available moisture. Precipitable water values are
forecast to drop to near normal and below normal values. Available
moisture will only increase under patches of more humid air moving
over the islands from time to time on Sunday and Monday, resulting
in passing showers over windward areas and possible western
afternoon convection. 925 mb temperatures should be at normal to
slightly above normal values.

&&

.LONG TERM (Tuesday through Saturday)...
Issued at 457 AM AST Sat Nov 1 2025

The long-term period appears to be dominated by variable weather
conditions. Based on the latest model guidance, the wind pattern
will be mainly influenced by a strong high pressure system over
the central Atlantic, promoting easterly winds for most of the
period. The pressure gradient will remain tight through at least
Tuesday night, as a result, breezy conditions are expected during
this time, followed by a decreasing trend on Wednesday and
Thursday.

At the mid to upper levels, a strong mid level ridge is expected
to persist and dominate most of the period, promoting stable and
drier conditions aloft. However, an upper level low moving south
of the area, over the Caribbean waters, will slightly weaken
atmospheric stability across the region and induce weak surface
troughs. According to the PWAT guidance, moisture content will
fluctuate from normal to below normal for most of the period, with
moisture mainly confined to the lower levels. This pattern will
allow patches of low level moisture to continue filtering into
Puerto Rico and the U.S. Virgin Islands. As a result, there will
be a low to medium chance (2040%) of occasional passing showers
over the windward portions of the U.S. Virgin Islands and eastern
Puerto Rico during the morning hours, followed by afternoon
convection across western Puerto Rico (5060%) driven by local
effects, available moisture, and marginal instability. At this
time, the flood risk is maintained at a limited level, primarily
for the western sectors of Puerto Rico each afternoon.
Additionally, a limited to no heat risk is likely to persist, as
indicated by a decreasing trend in the 500 mb and 925 mb
temperatures. This could support some thunderstorm development;
however, it will depend on the available moisture and the
persistence of the mid-level ridge.

&&

.AVIATION...
(06Z TAFS)
Issued at 457 AM AST Sat Nov 1 2025

Mainly VFR conds expected. SHRA/TSRA will continue to affect eastern
and southern terminals during period with brief MVFR conditions
possible, due to a tropical wave moving south of the area. During
the afternoon SHRA/TSRA could also form over central to W-NW PR and
affect TJSJ/TJPS/TJBQ with brief MVFR conditions possible. ESE winds
up to around 15 kts with higher gusts after 01/12Z, decreasing after
01/23Z. Drier conditions after 02/04Z.

&&

.MARINE...
Issued at 457 AM AST Sat Nov 1 2025

A surface high pressure system over the central Atlantic and a
tropical wave moving across the region today will promote moderate
to locally fresh trade winds through the weekend. Additionally,
thunderstorm activity is expected across the local waters and
passages as the tropical wave moves through the region. Wind-
driven, choppy to hazardous seas are expected from this evening
through early Sunday, particularly across the offshore Atlantic
waters, where a Small Craft Advisory is in effect. Winds and seas
are forecast to improve early next workweek.

&&

.BEACH FORECAST...
Issued at 457 AM AST Sat Nov 1 2025

A moderate risk of rip currents is expected through the weekend
at most beaches across Puerto Rico and the U.S. Virgin Islands.
Today, the moderate risk covers the northwestern, northern,
eastern, and southeastern beaches of Puerto Rico, including
Vieques, Culebra, and the U.S. Virgin Islands. Tonight, the risk
will extend to the southwestern beaches, and by Sunday, it will
include the southern beaches as well.

Beachgoers should exercise caution, as life-threatening rip
currents are possible along the surf zones. Additional hazards
include showers and thunderstorms developing across coastal areas.
Therefore, beachgoers should remain alert for sudden changes in
weather conditions and seek shelter immediately if thunder is
heard. Beachgoers are encouraged to continue monitoring the beach
forecast for updates or changes. For detailed information in your
area of interest, please visit weather.gov/beach.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...Small Craft Advisory from 6 PM this evening to 6 AM AST Sunday
     for AMZ711.

&&

$$

SHORT TERM/AVIATION...MRR
LONG TERM/MARINE/BEACH FORECAST...YZR