230
FXCA62 TJSJ 170846 CCA
AFDSJU

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
446 AM AST Wed Sep 17 2025

.KEY MESSAGES...

* A tropical wave combined with an upper level trough, will increase
  the frequency of showers and strong thunderstorms particularly
  today and Thursday. As a result, the risk of flooding will
  remain elevated. Additional hazards include rapid river rises,
  landslides, and frequent lightning.

* The Virgin Islands will also experience an increase in showers
  and thunderstorms, potentially leading to water surges in
  drainage guts, ponding on roadways, occasional lightning, and
  isolated landslides.

* Increasing heat risk is forecast again toward the end of the
  week and into the weekend.

* A moderate risk of rip currents is in effect for the northern
  and eastern beaches of Puerto Rico, as well as Culebra and St.
  Croix today and tonight. This weekend, Tropical Depression Seven
  is expected to move well northeast of the area as a Tropical
  Storm and could generate some swells, deteriorating marine and
  beach conditions.

&&

.SHORT TERM...Today through Friday...

Showers and thunderstorms along the leading edge of an approaching
tropical wave spread across most of the region overnight. Radar
estimates show peak rainfall near half an inch across the central
interior, and around a quarter of an inch across the northern and
eastern half of Puerto Rico, Vieques, Culebra, and the U.S. Virgin
Islands. Overnight lows stayed warm in the San Juan metro, the U.S.
Virgin Islands, and the local islands, ranging from 8082F, while
the central interior cooled into the low 60s. Winds were generally
from the east-northeast but remained mostly light and variable over
land, with brief gusts near showers and thunderstorms.

Unsettled and active weather is expected today as a tropical wave
interacts with an upper-level trough, keeping the atmosphere very
moist and unstable. Moisture levels are unusually high for this time
of year, peaking near 2.4 inches this morning, while cooler mid-
level temperatures support widespread showers and thunderstorms. The
most active period is expected this afternoon, especially across the
interior, west, and northwest Puerto Rico, though heavy rain is
possible across the entire region. Hazards include flooding in urban
areas, on roads, and along small streams, with a risk of flash
floods and landslides in steep terrain where soils are already
saturated. Thunderstorms may also bring frequent lightning and gusty
winds. Winds will shift from the east-northeast this morning to the
east-southeast by early afternoon at 1520 knots, carrying showers
and storms across the islands, with breezy to locally strong
conditions in the U.S. Virgin Islands, Vieques, Culebra, and eastern
Puerto Rico. Clouds and rain will help keep temperatures slightly
cooler than recent days, though humidity will remain high. Residents
in flood-prone or mountainous areas should stay alert for rapid
changes in weather, avoid flooded roads, and move to safe shelter if
thunderstorms approach.

Moisture and instability will continue tonight into Thursday,
keeping conditions favorable for more showers and thunderstorms.
Activity will focus on windward areas overnight, then shift back to
the interior and northwest Puerto Rico by Thursday afternoon. With
lighter winds from Thursday afternoon onward, storms will move more
slowly, prolonging the risk of flooding and landslides. By Friday,
moisture levels will return closer to normal and the atmosphere will
warm, leading to more localized rainfall, though isolated flooding
will still be possible. At the same time, southeasterly winds and
high humidity will bring back dangerous heat by the end of the week,
especially with fewer showers to provide relief. People should
remain cautious near rivers, small streams, and steep slopes, and
prepare for the heat by staying hydrated, limiting time outdoors,
and using shade or air conditioning whenever possible.


.LONG TERM...Saturday through Wednesday...

By Saturday, on of the systems the National Hurricane Center is
monitoring, recently formed Tropical Depression Seven, should be
located about 550 miles northeast of the area. If the forecast
track continues as expected, a col region over our area will
promote weak and variable winds at least through Tuesday night.
The latest model guidance suggests that precipitable water (PWAT)
values will remain within the average range for this time of year,
between 1.70 and 1.90 inches on Saturday, decreasing to between
1.25 and 1.50 inches by Sunday and Monday.

Under this scenario, expect morning showers across windward areas
of the islands, followed by afternoon showers and isolated
thunderstorms across the interior and western sectors of Puerto
Rico, fueled by diurnal heating and local effects. As a result, an
elevated flood risk is in place for Saturday, while the risk will
be more limited on Sunday and Monday, particularly across the
aforementioned areas. With soils already saturated in parts of
Puerto Rico due to recent rainfall and lighter winds expected
during this period, showers will likely move slowly, leading to
greater rainfall accumulations and an increased risk of flooding.
Urban and small stream flooding is likely to persist each day, and
some rivers may reach flood stage. In the Virgin Islands, periods
of showers and thunderstorms are expected to cause water surges
along guts and drainage channels, ponding on roadways, and
isolated urban flooding. Additional hazards include landslides,
frequent lightning, and gusty winds.

By Tuesday night, a wind surge is expected to approach the area,
bringing gusty winds and increasing moisture and rain chances for
the middle part of the week. Flood risk will likely remain
elevated. This wind surge appears to be associated with the second
tropical wave the National Hurricane Center is monitoring, which
currently has a 10 percent chance of formation in the next 48
hours and a 20 percent chance over the next seven days. At the
moment, it seems this system will remain trapped well east of our
region while surface high pressure dominates to the north. We will
continue to monitor this closely and provide updates as needed.

In terms of temperature, 925 mb temperatures are forecast to peak
at nearly two standard deviations above normal on Saturday and
remain near the 75th percentile from Sunday through early next
week. This pattern will elevate the heat risk across the region.
Heat Advisories or even Extreme Heat Warnings may be issued.
Residents and visitors are strongly advised to stay hydrated,
avoid prolonged sun exposure during peak heat hours, and take
extra precautions, particularly those without access to adequate
cooling or hydration.

&&

.AVIATION...
(06Z TAFs)

Increased SHRA/TSRA during the next 24 hours will bring periods of
MVFR with brief IFR conditions possible. Activity will mainly affect
TJSJ and USVI terminals through 17/15Z, then expand to most
terminals through the remainder of the forecast period. Trade winds
will veer from the southeast today, with winds at TAF sites starting
light to calm and variable this morning, increasing to 1520 kts
with gusts up to 2530 kts between 17/1422Z, before diminishing
again to light and variable after 17/22Z. Gusty winds are likely in
and near SHRA/TSRA.

&&

.MARINE...

Increased SHRA/TSRA during the next 24 hours will bring periods of
MVFR with brief IFR conditions possible. Activity will mainly affect
TJSJ and USVI terminals through 17/15Z, then expand to most
terminals through the remainder of the forecast period. Trade winds
will veer from the southeast today, with winds at TAF sites starting
light to calm and variable this morning, increasing to 1520 kts
with gusts up to 2530 kts between 17/1422Z, before diminishing
again to light and variable after 17/22Z. Gusty winds are likely in
and near SHRA/TSRA.

&&

.BEACH FORECAST...

Today, a moderate risk of rip currents continues across the north
and east-facing beaches of Puerto Rico, Culebra, and St. Croix,
while a low risk is expected elsewhere. Similar conditions are
expected to prevail through most of the workweek, so beachgoers
are advised to exercise caution at all times, as a moderate risk
means life-threatening rip currents are possible in the surf zone.
Additional hazards include afternoon thunderstorms. Remember, if
you hear thunder, seek shelter in a safe indoor location immediately.

By this weekend, some swells generated by Invest AL92 may further
deteriorate coastal conditions, leading to dangerous surf and an
increased rip current risk.

&&

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

$$

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

NWS SJU Office Area Forecast Discussion