National Weather Service Today's Weather Impact Levels

436
FXCA62 TJSJ 170915
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
515 AM AST Fri Oct 17 2025

.KEY MESSAGES...

* For Puerto Rico, there is a limited to elevated flood threat,
  with the heaviest showers expected through Sunday.

* For the U.S. Virgin Islands, shower and thunderstorm activity is
  forecast to continue throughout the day. Therefore limited
  flooding risk is forecast for the USVI.

* A gradual improvement in weather conditions is forecast by late
  Monday as a drier airmass moves across the islands.

* Northerly swells will lead to deteriorating seas and life-
  threatening rip currents during the weekend. Small craft
  advisories, rip current/high surf/coastal flood statements will
  be required, particularly from Sunday through Tuesday.

&&

.SHORT TERM...Today through Sunday...

During the night, a nearly stationary frontal boundary continued to
interact with deep tropical moisture over the northeastern
Caribbean, resulting in widespread heavy showers and numerous
thunderstorms, particularly across the Caribbean waters and the
Anegada Passage. Some of these storms extended into portions of St.
Croix, producing frequent lightning, gusty winds, and periods of
heavy rainfall. Several Special Marine Warnings were issued for the
affected waters, and a Special Weather Statement was issued for St.
Croix due to hazardous lightning and strong wind gusts.

For today, Friday, the frontal system will remain quasi-stationary
over the area, while a polar trough aloft maintains favorable
conditions for convection. Low-level winds will generally be from
the south-southwest, promoting moisture convergence across the
interior, north-central, and northeastern Puerto Rico this
afternoon, with localized flooding possible in these areas.
Additional impacts could extend into Vieques, Culebra, and portions
of the U.S. Virgin Islands. Model guidance indicates precipitable
water values (PWAT) near or slightly above climatological normals,
exceeding 2.0 inches. These moisture levels, combined with steep
lapse rates between 700-500 mb, will support strong to isolated near
severe convection during the afternoon and evening hours.

On Saturday, the frontal boundary and its associated trough aloft
will begin to weaken but linger over or slightly north of the area,
maintaining a moist and unstable pattern. Winds will veer more
southerly, favoring afternoon convection mainly across the interior
and north-central Puerto Rico. Although large-scale forcing will
gradually diminish, sufficient moisture and instability will remain
to support another round of showers and isolated thunderstorms.
Ponding of water on roadways and localized flooding will remain
possible, particularly where heavier downpours persist. Frequent
lightning and strong, gusty winds will be possible with the most
intense thunderstorms.

By Sunday, the remnants of the frontal system will shift farther
north as the polar trough weakens and ridging begins to build from
the east. Winds will become more southeasterly, promoting a gradual
drying trend, especially across the U.S. Virgin Islands and eastern
Puerto Rico. However, diurnal heating and lingering low-level
moisture will still trigger afternoon convection across the
northwestern quadrant of Puerto Rico, where the flood threat will be
most concentrated.

The presence of cloud cover due to the stationary front could limit
surface heating, which in turn may reduce the overall heat threat.
Weather conditions will continue to be monitored, and if significant
cloud clearing occurs during the morning hours, Heat Advisories may
be required and will be issued accordingly. A downward trend in the
heat threat is expected through the weekend.


.LONG TERM...Monday through Thursday...

A gradual improvement in weather conditions is expected beginning
late Monday as a drier air mass filters across Puerto Rico and
the U.S. Virgin Islands. Model guidance indicates precipitable
water (PWAT) values decreasing to around or slightly below normal
levels for this time of the year, while mid-level relative
humidity also trends near normal. This drier and more stable air
mass will promote a noticeable reduction in the frequency of
showers and thunderstorm activity across the region. However,
residual low-level moisture, combined with local effects and
daytime heating, will still result in isolated to scattered
afternoon showers, mainly across the interior and western Puerto
Rico each day. Overall, the flooding threat should remain limited
to none through midweek. This weather pattern should continue
through midweek.

By Thursday, model guidance suggests a gradual increase in PW,
relative humidity, and wind speed as a tropical wave or possible
tropical system moves near the local area. This will likely lead
to a return of wetter conditions by the latter part of the
workweek into the weekend. At this time, the National Hurricane
Center forecasts a 10 percent chance of development in the next 48
hours and a 30 percent chance within the next 7 days.

Regardless, residents and visitors are encouraged to continue
monitoring the latest forecasts for any significant changes in
conditions.

&&

.AVIATION...
(06Z TAFS)

A nearly stationary front ovr and to the N of the area will continue
to generate SHRA/TSRA ovr the waters. Mainly VFR thru prd. However,
low VIS/CIGs could result in brief MVFR/IFR in SHRA/TSRA ovr TAF
sites. Under S-SW steering winds, intermittent SHRA/TSRA may affect
TJPS/TJSJ/TIST with aftn convection. Sfc wnd S-SW 8-14 kt with brief
gusts 25-30 kt nr TSRA, bcmg lgt/vrb aft 23Z. WSW winds 10-20 kt blo
FL050 per 17/00Z sounding.

&&

.MARINE...

The nearby stationary boundary will continue to promote shower and
thunderstorm activity across the regional waters and passages through
the weekend. This will also increase wind speed from time to time
with the heaviest thunderstorm activity. Pulses of a long period
easterly swell will continue to reach the local exposed waters
through tonight. Another but stronger long period northerly swell,
associated to low pressure system over the northwestern Atlantic
waters, is expected to reach the Atlantic waters and local passages
around Sunday into the upcoming workweek. As a result, hazardous
marine conditions are anticipated. Please, continue to monitor the
forecast updates over the coming days.

&&

.BEACH FORECAST...

Pulses of long period northerly swells will gradually increase the
threat of life-threatening rip currents along the west, north,
and eastern beaches of the islands during the weekend. High surf
conditions and minor coastal flooding are likely by Sunday as the
northerly swell builds seas between 6 and 8 feet around 12 to 14
seconds, which translates to breaking waves between 10 and 15
feet. Overall, dangerous swimming conditions, minor beach
erosion, and life-threatening rip currents are expected from this
weekend into early next week.


&&

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

$$

SHORT TERM/AVIATION...CVB
LONG TERM/MARINE/BEACH FORECAST...MMC

NWS SJU Office Area Forecast Discussion