National Weather Service Today's Weather Impact Levels

498
FXCA62 TJSJ 171740
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
140 PM AST Wed Sep 17 2025

.KEY MESSAGES...

* For the rest of today into the evening, showers and
  thunderstorms will persist over the local waters due to the
  combined influence of a tropical wave and an upper-level trough
  just north of the region.

* A warming trend is expected to begin on Friday across the
  islands, with warmer conditions allowing heat indices to reach
  Heat Advisory criteria in coastal and urban areas.

* Across the U.S. Virgin Islands, a showery pattern will persist
  through the afternoon into the evening, leading to a limited
  increase in flood potential.

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

&&

.SHORT TERM...Rest of Today through Friday...

Shower activity diminished in the early morning hours, with some
remaining thunderstorms observed across the Caribbean waters and
around southeastern Puerto Rico. Some showers managed to form in the
interior and west. It was very warm too, with highs ranging from the
mid-80s to the low 90s across coastal areas of Puerto Rico and in
the Virgin Islands.

The axis of the wave was analyzed just to the east of the Virgin
Islands, where an extend area of above normal precipitable water is
observed in satellite-derived products. As this feature continues to
move westward, the winds will shift from the northeast, increasing
the potential for showers and thunderstorms across the local
islands. This afternoon, the focus of the rain should be around
western Puerto Rico, and also around the Virgin Islands and eastern
Puerto Rico. Although the rain is not expected to be widespread,
these areas that receive heavy rain can expect some urban and small
stream flooding, isolated mudslides, water surges along rivers, and
lightning and gusty winds.

Tonight and tomorrow, as the wave moves toward the Dominican
Republic, the wind flow is expected to shift from the southeast or
south-southeast. The focus of the rain then will be along the
southern and eastern half of Puerto Rico, while some showers will
also reach portions of the Virgin Islands, Vieques and Culebra.
Threats are impacts are expected to be similar, with rainfall
accumulations of 1 to 2 inches, and isolated higher amounts.

On Friday, the pressure gradient weakens, with a deep layer wind
flow from the south, and surface speeds around 10 kts or less. With
these winds, 925 mb temperatures will go up, again nearly two
standard deviation above the climatological mean. This translate
into very hot conditions, with a level of heat that affect anyone
without effective cooling or adequate hydration. Lighter south winds
should also focus the afternoon showers and thunderstorms along the
interior and the northwest quadrant of Puerto Rico. Again, urban and
small stream flooding, rapid river rises along rivers, and frequent
lightning are the main impact associated with the rain.

.LONG TERM...Saturday through Wednesday...
//from previous discussion//

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...
(18Z TAFs)

Brief period of MVFR conditions will remain possible in
and around TJBQ through 17/22z. Overnight...Passing showers may
affect the USVI terminals, nevertheless mainly VFR conditions
expected. Easterly winds 10 to 15 knots through 17/22z with sea
breeze variations, becoming light and variable overnight. Gusty
winds near showers.

&&

.MARINE...

A surface high-pressure system over the central and eastern Atlantic
will promote moderate to locally fresh easterly winds, becoming
light from Thursday night onward. Small craft should exercise
caution across the offshore waters and local passages through at
least tonight. A tropical wave moving across the region will result
in frequent showers and stronger thunderstorms over the local
waters, mainly today through Thursday. Additionally, swells
generated by Invest AL92, as it moves northeast of the region, could
further deteriorate marine conditions this weekend, increasing the
risk of hazardous seas.

&&

.BEACH FORECAST...

No changes were introduced to the coastal forecast. For the rest of
the day, the moderate risk of rip currents will  continue 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.

&&

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

$$

SHORT TERM...ERG
LONG TERM...YZR
AVIATION...OMS
MARINE/BEACH FORECAST...LIS

NWS SJU Office Area Forecast Discussion