National Weather Service Today's Weather Impact Levels

321
FXCA62 TJSJ 121815
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
215 PM AST Sun Oct 12 2025

.KEY MESSAGES...

* Showers and thunderstorms will persist for the rest of the
  afternoon across interior and western/northwestern Puerto Rico
  resulting in limited to elevated flooding risk, frequent
  lightning and gusty wind conditions.

* More stable weather conditions are expected in the next few
  days. However, by Thursday into around Saturday, conditions will
  turn more favorable for widespread showers and stronger
  thunderstorms resulting in an increased risk of urban and small-
  stream flooding, quick river rises, frequent lightning and
  gusty wind conditions.

* Southerly wind flow will bring above-normal temperatures in
  combination with above-normal moisture, which could result in an
  elevated to significant heat threat, particularly Tuesday
  onwards.

* A northerly swell could result in deteriorating marine and
  coastal conditions by next weekend.

* The U.S. Virgin Islands` biggest threats are heat during the
  upcoming week, with life-thretening rip currents and hazardous
  seas returning by the end of the week into the weekend.

&&

.SHORT TERM...Rest of Today through Tuesday...

A variable morning persisted across the islands with cloudiness and
some isolated passing showers across eastern Puerto Rico. As the
morning passed, heat indices along coastal areas increased, with
some stations reporting 111 degrees in the north central sections of
Puerto Rico and in the low 100s across the southern coastal plains
due to cloud cover. At 10 AM, satellite imagery showed cloudiness
developing along the mountains, resulting in showers along the
western interior sections of Puerto Rico.

For the rest of the short-term period, a gradual improvement in
weather conditions is expected as a high-pressure system dominates
all levels of the atmosphere, from the surface to the mid and upper
levels, strengthening stability across the region. This pattern will
favor a drier and more stable environment, with a decrease in
relative humidity between 850 and 700 MB, as indicated by recent
global model guidance, where values of moisture will remain in the
25th percentile. Under these conditions, vertical cloud development
will remain limited, and the likelihood of deep convection will be
low, limiting rainfall activity to brief and isolated afternoon
showers, mainly across the interior and western Puerto Rico due to
local effects and daytime heating. At the surface, the strengthening
high over the central Atlantic will maintain an east-southeast wind
flow, which is expected to increase slightly as the pressure
gradient tightens across the area. This will occasionally transport
patches of shallow moisture across the islands, although no
significant changes are anticipated in the overall weather pattern.

In terms of heat, a prolonged heat spell is forecast for the
upcoming days. Recent model guidance continues to indicate a steady
trend of a +2 standard deviation anomaly in 925 MB temperatures,
particularly on Tuesday. As a result, heat indices are expected
to range between 105 and 111 degrees Fahrenheit across coastal and
urban areas, particularly along the north, south, and east
coastal municipalities, as well as the Vicinity of Caguas. These
conditions will support a limited to elevated heat risk, with a
potential for significant heat impacts in densely populated areas.
Residents and visitors are urged to stay hydrated, take frequent
breaks in shaded or air-conditioned places, and avoid strenuous
outdoor activities during the peak heating hours of the day.

.LONG TERM...Wednesday through Sunday...

.PREV DISCUSSION... /issued 515 AM AST Sun Oct 12 2025/

At the beginning of the long-term period, we will be transitioning
into more favorable conditions for increased shower coverage and
stronger thunderstorms. The mid- to upper-level ridge will begin
to be replaced by a deep-layer trough, while 500 mb temperatures
cool, enhancing thunderstorm development during the afternoon
hours. On Wednesday, surface winds will be light with an easterly
to southeasterly component, then from Thursday onward, winds will
shift to a more southerly direction and remain light. On Wednesday,
afternoon convection is expected to develop over the interior and
move into the western sectors of Puerto Rico. Latest model
guidance indicates that precipitable water (PWAT) values will
remain near average through the period, ranging from 1.9 to 2.0
inches. From Thursday through Saturday, a frontal boundary will
approach and stall north of the area, while southerly flow steers
tropical moisture over the region. Relative humidity values in the
mid to upper levels will increase to above-normal levels.
Additionally, the southerly flow is expected to sustain an
elevated heat risk, with 925 mb temperatures showing values above
two standard deviations. Overall, expect typical afternoon
convection on Wednesday. However, from Thursday through Saturday,
the combination of the mentioned variables, better atmospheric
dynamics and moisture will support stronger afternoon
thunderstorms, increasing the potential for flooding across the
region. This includes flooding of urban areas, roads, small
streams, and washes. By Sunday, ridging is expected to begin
dominating the region once again.


&&

.AVIATION...

Brief MVFR conditions expected at TJBQ and TJPS due to afternoon
SHRA/TSRA. Elsewhere, mainly VFR conditions will prevail across the
local terminals. Ceilings will generally remain near FL030, but VIS
and CIGs will be reduced at times in and near SHRA/TSRA this
afternoon. Winds will persist from the E at 10-15 KT with higher
gusts, diminishing around 12/23Z, then increasing again from the E-
ESE at 10-20 KT across all TAF sites after 13/12Z.

&&

.MARINE...

Gentle to moderate east to southeast winds will prevail over the next
few days as the remnants of Jerry shift well north of the area and a
surface high pressure builds across the Central Atlantic. Above normal
moisture content will continue to result in showers and thunderstorms
across the waters this morning, and across the norwestern waters of
Puerto Rico this afternoon. Seas generally below 5 feet throughout
the forecast period.

&&

.BEACH FORECAST...

A moderate risk should return by tonight across beaches along the
northern and eastern coasts of Puerto Rico, Culebra and St.
Thomas. That means life-threatening rip currents are possible in
the surf zone and beachgoers need to exercise caution. Over the
coming days, similar conditions will dominate. For more
information, please refer to the Surf Zone Forecast for Puerto
Rico and the U.S. Virgin Islands (SRFSJU) or visit
weather.gov/beach.

Heed the advice of lifeguards, beach patrol flags and signs. If
you become caught in a rip current, yell for help. Remain calm, do
not exhaust yourself and stay afloat while waiting for help. If
you have to swim out of a rip current, swim parallel to shore and
back toward the beach when possible. Do not attempt to swim
directly against a rip current as you will tire quickly.

In addition, thunderstorms will pose significant hazards at the
coast. Frequent lightning strikes, gusty winds, and heavy rainfall
may lead to dangerous conditions, including sudden reductions in
visibility and localized flooding near the shoreline. Remember: if
thunder roars, go indoors. Swimmers and boaters should immediately
seek shelter when storms approach.

&&



.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...LIS
MARINE/BEACH...CVB

NWS SJU Office Area Forecast Discussion