344
FXCA62 TJSJ 170711
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
311 AM AST Tue Mar 17 2026

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

.KEY MESSAGES...
Issued at 258 AM AST Tue Mar 17 2026

* Hazardous marine and coastal conditions will persist through
  much of the week. Small Craft Advisories remain in effect for
  several local waters, and a high risk of rip currents is
  expected for many northern and eastern beaches of Puerto Rico
  and the U.S. Virgin Islands.

* A front and associated trough will increase showers during the
  weekend.

* Across the USVI, passing showers will increase late this
  afternoon through the evening hours. Breezy conditions expected
  early in the day.

&&

.Short Term(Today through Thursday)...
Issued at 258 AM AST Tue Mar 17 2026

A generally drier air mass continues to prevail across the region
today. Total Precipitable Water satellite imagery confirms that
Puerto Rico and the U.S. Virgin Islands are currently sitting in
an area of relatively lower moisture. The latest forecast
soundings show precipitable water (PWAT) values hovering near 1.0
inch today before gradually recovering. Because of limited
moisture and breezy low-level winds, with 925 mb wind speeds
starting the day around 25 knots, any showers that do develop will
be fast moving and produce only minor rainfall accumulations. Hi-
res model guidance supports this dry trend, showing localized
accumulations mostly remaining under 0.20 inches through the day.

Between late tonight and through early Wednesday morning, wind
speeds will gradually decrease into the 15 to 20 knot range. At
the same time, a weak trade wind perturbation will move through,
bringing a brief surge in moisture that pushes PWAT values back
toward climo normals at around 1.40 inches. Residents can expect a
slight increase in shower activity associated with this moisture,
primarily focused across the USVI and eastern sections of PR.
Rainfall totals are forecast to remain relatively light, with isolated
spots potentially seeing up to half an inch. An upper level ridge
will continue to promote stable conditions aloft, and flood
concerns will remain low.

By Thursday, the weather pattern will become somewhat more active
as deeper moisture pools over the islands. The GFS soundings show
PWAT values rising further to 1.50-1.70 inches, accompanied by a
sharp increase in mid-and low-level relative humidity.
Furthermore, the trade winds will continue to subside, with 925 mb
speeds dropping into the 10 to 15 knot range. This combination of
lighter steering flow and increased atmospheric moisture will
support a more typical shower pattern; ensemble rainfall models
indicate enhanced precipitation coverage across the area, with
localized accumulations potentially reaching near an inch.

&&

.Long Term(Friday through Tuesday)...
Issued at 258 AM AST Tue Mar 17 2026

Variable conditions are expected in the long-term forecast. A broad
surface high pressure over the Central Atlantic will promote winds
with a southerly component, with patches of moisture across the CWA
on Friday. This will bring passing showers over windward sections in
the morning, with afternoon showers over north/northwestern Puerto
Rico. Rainfall accumulations should remain limited, leading to
ponding of water over roadways and poorly drained areas. Weather
conditions will likely become wetter and more unstable in the
upcoming weekend, as a deep-layered trough with an associated
frontal boundary will likely approach the region by Saturday,
inducing a pre-frontal trough that will likely increase shower and
thunderstorm activity. Additionally, a col region will move across
the region by Saturday, with 925 mb winds plummeting to well below
normal (mostly variable and calm winds). According to the latest
model guidance, Precipitable Water values are expected to range
between 1.5 and 1.75 inches, which is above the climatological
normal, with the best moisture content in the low and mid levels
(above 70%), increasing chances of scattered to numerous showers.
Additionally, weakening winds will result in stationary showers and
thunderstorms, with the highest potential of flooding on Saturday
and Sunday. Due to the approach of the trough, the mid-level
temperatures should slightly cool (around -8 degrees Celsius), with
a jet streak positioning over the region, allowing ventilation aloft
(between 70 and 90 kt).  Although the best of convection should
remain north of the CWA, conditions will likely be favorable for
deeper convection and increasing lightning potential. Therefore, the
most likely scenario is an advective pattern on both Saturday and
Sunday, with afternoon convection over the mountain ranges of Puerto
Rico. Rainfall accumulations will likely result in urban and small
streams flooding, with a low chance of flash flooding, over the
aforementioned areas. By Monday, another surface high pressure
exiting eastern CONUS will increase pressure gradient, promoting E-
ENE winds. Weather conditions should gradually improve; however,
remaining moisture content should be enough for the development of
showers across the regional waters into windward sections throughout
the day, along with afternoon convection. Residents and visitors are
encouraged to continue to monitor the weather forecast due to
discrepancies between global solutions.

Although Friday will likely be the warmest day of the long-term,
maximum temperatures should remain in the mid to high 80s, with
localized low 90s, across low elevation areas of the islands, with
no heat threat expected.

&&

.AVIATION...
(06Z TAFS)
Issued at 258 AM AST Tue Mar 17 2026

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, by 17/20z -SHRA embedded in the
trade winds will reach the USVI terminals, and shortly after the
eastern PR terminals. This may lead to brief MVFR cigs and mostly
VCSH/-RA periods. Winds will prevail from the E to ESE at 15-20
kt with gusts in the low 30s.

&&

.MARINE...
Issued at 258 AM AST Tue Mar 17 2026

The pressure gradient across the region will gradually loosen today
and continue to diminish through the rest of the week. However,
moderate to fresh easterly winds will persist across the regional
waters. As a result, mariners can expect choppy to rough seas across
much of the local waters. Therefore, Small Craft Advisories will
remain in effect for most of the regional waters today. An easterly
perturbation will increase shower activity across the regional
waters around today. A frontal boundary along the eastern seaboard,
moving eastward, will approach the northeast Caribbean later in the
week, further easing the pressure gradient from Thursday through the
end of the workweek.

&&

.BEACH FORECAST...
Issued at 258 AM AST Tue Mar 17 2026

Beach conditions will remain dangerous for inexperienced beachgoers
across most of the local islands. Although winds are expected to be
lighter than yesterday, lingering easterly winds will continue to
generate choppy to rough seas across the regional waters. This will
maintain elevated wave action along exposed beaches. As a result, a
high risk of rip currents will persist for many of the exposed
beaches across the islands, leading to dangerous swimming conditions.

Beachgoers should remain alert to changing coastal conditions and
continue monitoring the latest forecasts and statements. For
additional information, please visit: weather.gov/beach/sju.


.FIRE WEATHER...
Issued at 258 AM AST Tue Mar 17 2026

A Fire Danger Statement will be issued once again for the coastal
plains of southern Puerto Rico. The KBDI in Cabo Rojo was at 687
and 552 in Guanica. Southeast winds should prevail between 14 and
22 mph with gusts close to 30 mph. Passing light showers are
expected early this morning, but drier air is expected throughout
the day, dropping relative humidities between 45-55% along the
south coast of PR. Therefore, the fire danger is elevated today
across southern PR.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Wednesday afternoon for PRZ001>003-
     005-007-008-011>013.

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

AM...Small Craft Advisory until 6 PM AST Wednesday for AMZ711-712-716-
     723-726-733-735-741.

&&

$$

SHORT TERM...DS
LONG TERM....MNG
AVIATION...DS

NWS SJU Office Area Forecast Discussion