679
FXCA62 TJSJ 181906
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
306 PM AST Wed Mar 18 2026

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

.KEY MESSAGES...
Issued at 305 PM 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 the rest of the afternoon.
  Similar conditions are expected on Thursday.

* 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(This evening through Friday)...
Issued at 305 PM AST Wed Mar 18 2026

Afternoon showers have developed under breezy to locally windy
ESE steering flow as a shallow patch of moisture is moving over
the region. These showers have developed mainly over interior to
W-NW PR but also over sectors of S, N and E PR, as well as mainly
downwind of the USVI. Low concentrations of Saharan dust are also
present and will continue to reach the region through the short
term period. ESE steering flow will continue gradually decreasing
tonight and through the short term period, being around 15 kts by
this evening. Although PWAT values will generally be at normal to
below normal values (around an inch to 1.30 inches), patches of
both more humid and drier air will continue to reach the islands
through tomorrow. Current model guidance suggests that a patch of
moisture will reach the southeastern region late tonight into
tomorrow morning, increasing shower frequency over the area,
particularly SE PR, prompting a limited flooding risk over that
area. Afternoon showers will develop at similar areas as today,
however the slower steering flow can help increase rainfall
accumulations, prompting a limited flooding risk mainly over W-NW
PR, with lighter accumulations expected across the USVI and the
rest of PR.By Friday and into the long term period, an increase in
PWAT values and overall humidity. PWAT values will increase to
normal values to start the day and above normal values (1.50 to at
least 1.75 in) by Friday afternoon into Friday night as a frontal
boundary and associated trough approach the area. SE winds will
continue decreasing, with 925 mb winds forecast to drop to 5 to 10
kts. This wind direction and lower speeds are forecast to promote
warm to hot temperatures on Friday. 925 mb temperatures can reach
2 standard deviations above normal on Friday higher than the more
seasonal values this afternoon and tomorrow. Stronger and slow-
moving afternoon showers are possible over the northwest quadrant
of PR and downwind of the local islands and El Yunque, prompting a
limited to elevated flooding 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...
(18Z TAFS)
Issued at 305 PM AST Wed Mar 18 2026

Mainly VFR conditions will prevail under ESE flow at 15 to 20
kts. -SHRA/VCSH will continue to affect the area through this
afternoon with a patch of moisture moving in late tonight towards
tomorrow morning, increasing -SHRA/VCSH frequency over the E and
SE region. These can lead to brief MVFR conditions. Winds
decreasing after 18/23Z, especially for PR terminals, increasing
again to around 10 to 15 kts with higher knots after 19/13Z.


&&

.MARINE...
Issued at 300 PM AST Wed Mar 18 2026

The pressure gradient across the region will continue to weaken
through the rest of the week. However, moderate to locally fresh
easterly winds will persist across most local waters and passages
tonight, resulting in seas of 4 to 6 feet. As a result, small
craft operators should exercise caution. A Small Craft Advisory
will remain in effect through Thursday afternoon across the
offshore Atlantic waters due to seas up to 7 feet. 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.
This will bring gentler winds but increasing chances of rain.

&&

.BEACH FORECAST...
Issued at 305 PM AST Wed Mar 18 2026

Tonight through Thursday, life-threatening rip currents are
likely along the northern, eastern, and southeastern beaches of
Puerto Rico, as well as in Culebra, Vieques, and the U.S. Virgin
Islands. As a result, a High Rip Current statement remains in
effect at least through Thursday afternoon for these areas. A low
to moderate risk of rip currents persists along the western and
southeastern beaches of Puerto Rico, meaning that life-threatening
rip currents are still possible in the surf zone.

From Friday onward, as winds become significantly lighter, a
moderate risk of rip currents will prevail along north-facing
beaches of Puerto Rico, Culebra, and the U.S. Virgin Islands,
while a low risk is expected along more protected southern
beaches. Remember that even when the risk is low, life-threatening
rip currents can still occur near groins, jetties, reefs, and
piers. Residents and visitors are encouraged to monitor the
forecast for updates or changes. For additional information and
location-specific rip current details, please visit:
weather.gov/beach/sju.

&&

.FIRE WEATHER...
Issued at 305 PM AST Wed Mar 18 2026

From late morning into early afternoon, some surface stations,
especially across southwestern Puerto Rico, reported minimum
relative humidity in the low to mid-50% range. Sustained winds
ranged from 10 to 18 mph, with occasional gusts of 22 to 27 mph.
Relative humidity is expected to increase through the afternoon,
reducing the overall risk. A RFD will not be issued at this time,
however, partners should continue monitoring conditions on
Thursday, as similar weather is expected. By late week into the
weekend, a frontal boundary and associated trough will bring
increased moisture to the area.

&&

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

     High Rip Current Risk until 6 PM AST this evening 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/AVIATION...MRR
LONG TERM...MNG
MARINE/BEACH/FIRE...YZR

NWS SJU Office Area Forecast Discussion