Hurricane Season runs from June 1-November 30
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802
FXCA62 TJSJ 200904
AFDSJU
Area Forecast Discussion
National Weather Service San Juan PR
504 AM AST Thu Nov 20 2025
...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST...
.KEY MESSAGES...
Issued at 458 AM AST Thu Nov 20 2025
* Life-threatening rip currents are expected to form along the
north-facing beaches in Puerto Rico, Culebra, and the eastern
half of St. Croix.
* Residents and visitors in the USVI and PR can expect pleasant
temperatures as a cooling trend will prevail, especially from
Friday into next week.
* There is a slight risk of afternoon thunderstorms between today
and tomorrow (Friday).
&&
.Short Term(Today through Saturday)...
Issued at 458 AM AST Thu Nov 20 2025
An active weather pattern affected the region overnight, driven by a
passing trough aloft and abundant moisture associated with the
remnants of an old frontal boundary pushed southward by persistent
NE winds. Doppler radar showed scattered to numerous showers and
isolated thunderstorms, mainly over the surrounding waters, with
some of this activity spreading into northern and eastern Puerto
Rico, as well as Vieques, Culebra, and the U.S. Virgin Islands.
Since last evening, rainfall accumulations peaked near one inch in
very isolated areas of eastern Puerto Rico; however, no flooding
impacts were reported. Temperatures fell into the mid-70s across
lower elevations and the low-60s over higher terrain. Winds over
land were generally light to calm and variable through the night.
A broad polar trough over the westerncentral Atlantic continues to
send shortwave energy across the northeastern Caribbean. The first
shortwave will cross the region today, maintaining cooler-than-
normal mid-level temperatures and enhancing instability ahead of and
along the wave axis. Behind it, strengthening upper-level winds will
support a developing jet streak later today. At the surface, a
trough to the east-northeast and high pressure over the western
Atlantic will maintain NNE to NE trades, helping push the remnants
of an old frontal boundary southward toward the region. PWAT values
will remain near seasonal levels through the morning and early
afternoon, and combined with this moisture and lingering instability
will support scattered to locally numerous showers and isolated
thunderstorms, mainly across southwestern Puerto Rico. Across the
U.S. Virgin Islands, trade-wind showers and a few thunderstorms may
also affect the area at times. The main hazards today are lightning
and locally excessive rainfall, with a limited to locally elevated
flooding risk where convection persists.
A second, deeper shortwave is forecast to drop farther south on
Friday, bringing another brief period of cooling aloft before
quickly shifting east of the region. Once this wave clears,
subsidence and significant drying will dominate, with steady mid-
level warming and PWATs dropping below and well below typical values
between Friday evening and Saturday. A surface trough and a
strengthening high over the western Atlantic will reinforce NE trade-
wind flow, pushing increasingly drier air over the region. At the
same time, mid-level ridging will gradually strengthen the trade-
wind cap inversion, creating increasingly unfavorable conditions for
deep convection. Together, these features will mark the beginning of
a more stable and much drier period. Isolated nocturnal and early-
morning trade-wind showers will still occur due to shallow
instability from mild cold-air advection over warm waters, but
measurable rainfall will remain limited. Afternoon convection will
also be sharply reduced. Temperatures will trend slightly cooler
over the next few days, with daytime highs moderated by persistent
NE winds and overnight lows influenced by clearer skies. These
conditions may bring the first hint of a frito navideo by Friday
into the weekend. Overall, hazard risks will decrease significantly,
with only a limited risk of thunderstorms or flooding on Friday and
little to no risk on Saturday.
&&
.Long Term(Sunday through Thursday)...
Issued at 458 AM AST Thu Nov 20 2025
Forecast confidence remains low to moderate due to notable
discrepancies between the GFS and ECMWF regarding the evolution of
mid- to upper-level features early next week. These differences
directly affect expectations for instability and convective
coverage across Puerto Rico and the U.S. Virgin Islands.
The GFS suggests a short-wave trough replacing the zonal flow
aloft Sunday into Monday, followed by additional amplification on
Tuesday. This scenario would shift a mid-level ridge westward over
the Bahamas/Cuba, placing PR/USVI between the ridge to the west
and a deepening trough to the east, favoring increased upper-level
divergence and a more unstable environment. Under this
configuration, the probability of scattered afternoon convection
and isolated thunderstorms would be moderate (20-40%), peaking
Tuesday through the middle of the week.
In contrast, the ECMWF maintains a more stable pattern, with
zonal flow on Sunday and only weak short-wave perturbations on
MondayTuesday. Notably, the model retains the mid-level ridge,
supporting dry air intrusions and subsidence that would limit
convective development. Under this solution, afternoon showers
would be more isolated (2030%), primarily driven by local sea-
breeze and orographic effects. Given these differences, the
forecast leans on a climatological trade- wind pattern. Therefore,
expect periodic patches of moisture embedded in the trades
producing passing showers across the local waters, USVI, and
windward/eastern Puerto Rico. Each afternoon, isolated to
scattered convection (mainly interior and western PR) remains
possible, but the probability of thunderstorms stays low to
moderate (1030%), highest if the GFS scenario materializes.
Overall, no strong signal is emerging for widespread rainfall or a
significant instability event at this time, and uncertainty
remains elevated until better model consensus develops.
Local temperatures will continue to cool, remaining slightly below
normal, around the 25th percentile compared to November
climatology.
&&
.AVIATION...
(06Z TAFS)
Issued at 458 AM AST Thu Nov 20 2025
SHRA/iso TSRA will continue ovr the waters and nr TJSJ/USVI tmnls
thru the prd. Aftn CNVTN will expand toward TJPS, while SHRA may
persist at othr tmnls. Brief MVFR psbl due to MTN OBSC/reduced VIS,
mainly at TJPS/TJBQ. SHRA will dcrs aft 20/22Z but may linger nr
TJSJ/USVI ovrngt. Although overall steering flow remains NE, SFC
winds will be LGT/CALM and VRB early, bcmg 1015 kt btwn 20/1322Z,
then rtnng to LGT/VRB ovrngt.
&&
.MARINE...
Issued at 458 AM AST Thu Nov 20 2025
A long period north-northeasterly swell will continue to move across
the local waters through this evening. An upper-level short-wave
trough will help to promote afternoon thunderstorms across the Mona
Passage and Caribbean waters. The remnants of the frontal boundary
will slowly dissipate across the western Atlantic through Friday,
when a surface high is expected to build over the region. This high
pressure will promote moderate trade winds from the upcoming weekend
into early next week.
&&
.BEACH FORECAST...
Issued at 458 AM AST Thu Nov 20 2025
Based on buoy observations, the high risk of rip currents has
been extended through this evening due to lingering energy from a
fading north-northeasterly swell with a period of 11 to 13
seconds. This situation can lead to life-threatening rip currents,
particularly along the exposed north and east-facing beaches in
Puerto Rico, Culebra, and the eastern half of St. Croix. The rip
current risk is forecast to improve, becoming moderate over the
weekend and into early next week. However, another north-easterly
swell is likely to increase the risk to high levels again by
Tuesday.
Beachgoers are strongly encouraged to swim near a lifeguard, as
life-threatening rip currents are possible in the surf zone. For
location-specific information, visit weather.gov/beach/sju.
Additionally, beachgoers should be aware of other potential
hazards, such as lightning and gusty winds, due to showers and
thunderstorm activity expected this afternoon and tomorrow
(Friday) in coastal areas. Remember: If thunder roars, go indoors!
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through this afternoon for PRZ001-002-005-
008-012.
VI...High Rip Current Risk through this afternoon for VIZ002.
AM...None.
&&
$$
SHORT TERM/AVIATION...ICP
KEY MESSAGES/LONG TERM/BEACH FORECAST/MARINE....CAM
