National Weather Service Today's Weather Impact Levels

285
FXCA62 TJSJ 141839
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
239 PM AST Tue Oct 14 2025

.KEY MESSAGES...

* A wetter and unsettled weather pattern is forecast from
  Thursday into the weekend, as a deep-layered trough and a
  frontal boundary moves just north of the islands.

* An elevated heat threat is expected once again tomorrow across
  the coastal municipalities.

* For the U.S. Virgin Islands, heat related impacts are expected
  on Wednesday, with an increase in shower activity from Thursday
  onward.

* A northerly swell will lead to deteriorating marine and coastal
  conditions by the end of the week into next week.


&&

.SHORT TERM...Rest of today through Thursday...

Mostly sunny skies prevailed through the morning hours across the
islands. Isolated showers were developing early in the afternoon
hours over portions of the northwestern quadrant of PR, and
downwind of the USVI and eastern PR. Isolated thunderstorms are
still expected to develop mainly over northwest PR this afternoon.
Maximum temperatures were from the upper-80s to low-90s across
the lower elevations of the islands with heat indices between
105-110F. Winds were from the southeast up to 15 mph.

A mid-to upper-level trough over the western Atlantic will
gradually replace the ridge aloft and promote more unstable
conditions, particularly on Thursday. Meanwhile, at the surface,
an associated front and pre-frontal trough will increase moisture
content and promote a deep southerly steering wind flow over the
northeastern Caribbean. This will cause an increase in afternoon
shower and thunderstorm activity over the north-central and
eastern portions of PR, where the flood threat will be elevated on
Wednesday afternoon, and increasing in coverage on Thursday. Also,
an elevated heat threat with Heat Advisory conditions are likely
once again on Wednesday across most coastal municipalities of PR
and across the USVI.


.LONG TERM...Friday through Tuesday...

/From prev discussion issued at 517 AM AST Tue Oct 14 2025/

No major changes were introduced to the long-term forecast. A wet
and unstable weather pattern is expected for the upcoming weekend,
which may improve for the first part of the workweek. Winds should
remain light on Friday and Saturday, shifting from the southwest
influenced by a surface high pressure system over the central
Atlantic and a broad polar trough, which will pool the remnants
of the frontal boundary and high tropical moisture. From the
latest deterministic guidance of the GFS and the ECMWF,
Precipitable Water (PWAT) values should remain seasonal to above
climatological normal (2.0 - 2.2 inches). Additionally, the polar
trough reflected in the mid to high levels may deepen enough to
cool 500 mb temperatures (-6.5 to -7.5 degrees Celsius),
increasing instability and supporting deep convection. The Galvez-
Davison Index (GDI) also suggests the potential of isolated to
scattered thunderstorms through at least Sunday. Hence, the
frequency of showers and thunderstorms should remain high,
affecting mostly windward sections during the night through early
mornings, with deep convection activity remaining over the
mountain ranges of Puerto Rico in the afternoons. Winds should
increase and turn from the southwest as the surface high pressure
migrates west and approaches the CWA. Due to abundant moisture
content over the area, afternoon convection should concentrate
over northwestern Puerto Rico. Given the expected conditions, the
lightning and flooding threat will remain limited to elevated
during that period.

An improvement in weather conditions is expected by late Monday due
a drier air mass filtering into the region. The latest model
guidance shows a decrease in PWAT values (1.7 - 1.9 inches),
although theres high variability between ensemble members due to a
tropical wave that global models suggest should move south of the
CWA. Nevertheless, the combination of daytime heating, local
effects, and available moisture will enhance shower and thunderstorm
activity, mainly over the western/northwestern portions of Puerto
Rico; however, the flooding threat should remain limited.

The latest model guidance indicates that Sunday may be the
warmest day of the long-term period, followed by a gradual
decrease in 925 mb temperatures for the remainder of the period.
Nevertheless, heat indexes are still very likely to reach 100
degrees and may meet Heat Advisory Criteria. Hence, the heat
threat will remain elevated for the long-term forecast.


&&

.AVIATION...

(18Z TAFS)

Mainly VFR conditions are expected to prevail across
all terminals during the next 24 hours. However, tempo MVFR conds
are expected at TJBQ thru 14/22z due to SHRA/TSRA. Elsewhere,
mostly VCSH expected. The 14/12z TJSJ sounding indicated ESE winds
btw 4-21 kt fm the sfc to 4000ft.


&&

.MARINE...

A broad surface high pressure north of the region will maintain
moderate east to southeast trade winds today. Then, winds will
become light to gentle from the south-southwest Wednesday onwards.
A frontal boundary approaching the region will induce a pre-frontal
trough for the second half of the workweek, increasing shower and
thunderstorm activity across the regional waters and passages.
Pulses of a long period northerly swell will reach the Atlantic
waters and passages from Friday into early next week.


&&

.BEACH FORECAST...

There is a moderate risk of rip currents along the north and
eastern coast of Puerto Rico. Similar conditions are expected
during the next few days. However, by late Friday into Sunday,
pulses of a long period northerly swell will increase the threat
of life-threatening rip currents along the north coast of Puerto
Rico, and the US Virgin Islands.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007-
     008-010>013.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...None.
&&

$$

SHORT TERM/AVIATION...DSR
LONG TERM...MNG
KEY/MARINE/BEACH...LIS

NWS SJU Office Area Forecast Discussion