National Weather Service Today's Weather Impact Levels

770
FXCA62 TJSJ 180534 CCA
AFDSJU

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
134 AM AST Wed Mar 18 2026

...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST, FIRE WEATHER...

.KEY MESSAGES...
Issued at 130 AM AST Wed Mar 18 2026

* Hazardous seas and life-threatening rip currents will
  continue through at least Thursday.

* Breezy conditions and passing showers are expected across the U.S.
  Virgin Islands and Puerto Rico today.

* A frontal boundary and associated trough will increase shower
  activity from late this week into the weekend, bringing periods
  of unsettled weather across Puerto Rico and the U.S. Virgin
  Islands.

&&

.Short Term(Today through Friday)...
Issued at 130 AM AST Wed Mar 18 2026

A relatively dry and breezy pattern will continue across the region
today. Minor concentrations of Saharan dust may lead to hazy skies
today. Low-level winds remain elevated early this morning but will
gradually decrease from around 15 to 20 knots down toward 15 knots
by this evening. Trade winds will continue to bring pockets of
dry/moist air at times through Thursday. Therefore, with limited
moisture and breezy conditions, shower activity will be minimal;
ensemble rainfall models for today indicate light accumulations,
generally under a quarter of an inch, favoring eastern and
southeastern Puerto Rico, and the U.S. Virgin Islands. The
precipitable water content is expected to fluctuate between 1.00 and
1.25 inches through tomorrow. However, by late Thursday, a
transition begins as steering winds weaken significantly and
moisture slowly rebounds. The 925 mb winds will drop to around 10
knots, and PWAT values are expected to climb near 1.50 inches.
Therefore, this lighter wind regime and increasing moisture will
support afternoon shower development, predominantly over western and
northwestern Puerto Rico, where hi-res ensemble model guidance
suggests localized rainfall accumulations potentially reaching up to
an inch. At the same time, lighter rainfall accumulations are
expected across the USVI and the rest of Puerto Rico.

Heading into Friday, a substantial surge in deep moisture is
expected, with PWAT nearing 1.75 inches and mid-level relative
humidity spiking to near 80 percent. A prefrontal trough developing
over and just north of the region will promote lighter winds, around
5 knots, and more southeasterly winds. Warmer to hot temperatures
are expected, compared to previous days, and stronger afternoon
showers can develop over the northwest quadrant of PR, where the
slow-moving showers will enhance the flood threat.


&&

.Long Term(Saturday through Wednesday)...
Issued at 130 AM AST Wed Mar 18 2026

No major changes were introduced to the long-term forecast, with
unsettled conditions expected over the upcoming weekend. A deep-
layered trough with an associated frontal boundary is still forecast
to approach the local area by Saturday, inducing a prefrontal trough
that should increase shower activity and potential for isolated
thunderstorms. From the deterministic guidance of the GFS and ECMWF,
theres a medium chance of PWAT values increasing to above
climatological normal (1.6 - 1.8 inches), with a low chance of
reaching 2.0 inches. Additionally, ensemble members are tending to
higher low to mid-level moisture content. Model guidance keeps to
suggest that winds will likely weaken and remain variable as the
frontal boundary approaches and a col region  moving across the CWA.
As mentioned in the previous discussion, any shower development
could become stationary and produce higher rainfall accumulations.
Due to the influence of the trough, slightly cooler than normal 500
mb temperatures (between -8.5 and -9 degrees Celsius), a jet streak
in the upper levels (between 70 and 80 knots), and divergence aloft,
allowing cloud growth and ventilation. Given the expected favorable
conditions, deep convection is expected Saturday afternoon over the
mountain ranges of Puerto Rico, with showers and isolated
thunderstorms resulting in urban and small streams flooding. As
winds gradually increase and become from the NE, an advective
pattern should persist on Saturday night into Sunday morning,
increasing frequency of showers over windward sections of the
islands. These areas can expect ponding of water over roadways and
poorly drained areas. Afternoon convection on Sunday afternoon will
mostly concentrate over the mountain ranges into south/southwestern
portions of Puerto Rico, with an elevated risk of flooding as well.
A surface high pressure migrating into the western Atlantic on
Monday, but theres uncertainty as global solutions have
discrepancies. The GFS suggests moisture content enough for the
development of shower activity in the 1000 - 700 mb layer, while the
ECMWF shows drier than normal conditions. Due to local effects,
shower development cannot be ruled out, the flooding threat should
remain limited on Monday and none for the rest of the forecast.
Residents and visitors are encouraged to continue to monitor the
weather forecast, as uncertainty remains high for the next workweek.

&&

.AVIATION...
(06Z TAFS)
Issued at 130 AM AST Wed Mar 18 2026

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, brief trade winds showers could
move at times across the USVI and eastern PR terminals. Low-level
winds will continue from the ESE at 15-20 kt.

&&

.MARINE...
Issued at 130 AM AST Wed Mar 18 2026

The pressure gradient across the region will gradually weaken
through the rest of the week. However, moderate to fresh easterly
winds will persist across the regional waters today. As a result,
mariners can expect choppy to rough seas across much of the local
waters, with Small Craft Advisories remaining in effect for most
of the regional waters. A frontal boundary moving eastward along
the eastern seaboard will approach the northeastern Caribbean
later in the week, further relaxing the pressure gradient from
Thursday through the end of the workweek.

&&

.BEACH FORECAST...
Issued at 130 AM AST Wed Mar 18 2026

Beach conditions will remain hazardous for inexperienced swimmers
across much of the local islands. Breezy to windy easterly winds
will continue to generate choppy to rough seas across the regional
waters, increasing wave action along exposed beaches. As a result, a
high risk of rip currents will persist along many exposed beaches in
Puerto Rico and the U.S. Virgin Islands through much of the week.

Beachgoers should exercise caution, remain aware of changing coastal
conditions, and monitor the latest forecasts and statements. For
additional information, visit: weather.gov/beach/sju

&&

.FIRE WEATHER...
Issued at 130 AM AST Wed Mar 18 2026

The fire danger today will remain relative low as brief surge in
low-level moisture is cross the islands this morning. This could
keep relative humidities from dropping to critical fire weather
thresholds. However, breezy conditions will continue along the
southern coast of PR, where KBDI values remain well above critical
levels, particularly in Cabo Rojo at 689.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Thursday afternoon for PRZ001>003-
     005-008-012-013.

     High Rip Current Risk through this afternoon for PRZ007-011.

VI...High Rip Current Risk through Thursday afternoon for VIZ001-002.

AM...Small Craft Advisory until 6 PM AST Thursday for AMZ711.

     Small Craft Advisory until 6 PM AST this evening for AMZ712-716-
     723-726-733-735-741.

&&

$$

SHORT TERM...DSR
LONG TERM....MNG
AVIATION...DSR
BEACH/MARINE...ICP
FIRE...DSR

NWS SJU Office Area Forecast Discussion