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944
FXCA62 TJSJ 211803
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
203 PM AST Wed Oct 21 2026

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

.KEY MESSAGES...
Issued at 159 PM AST Wed Oct 21 2026

- Weather conditions will become increasingly wet and unstable
  tonight through the weekend, with more frequent showers and
  thunderstorms, including during the nighttime hours.

- Periods of heavy rainfall may lead to ponding of water on
  roads, urban and small-stream flooding, rapid river rises, and
  isolated flash flooding. Thunderstorms may also produce frequent
  lightning and gusty winds. Landslides will become an increasing
  concern in areas receiving repeated rainfall.

- A High Risk of Rip Currents continues through this evening
  along north-facing beaches. Conditions will briefly improve
  Thursday before another swell brings a renewed high rip current
  risk Friday through the weekend, with potentially hazardous
  breaking waves. Beachgoers should avoid swimming at affected
  beaches.

- More frequent showers and thunderstorms Thursday through the
  weekend will increase the risk of lightning near beaches and
  coastal areas. Seek shelter indoors when thunderstorms approach.

&&

.Short Term(This evening through Friday)...
Issued at 159 PM AST Wed Oct 21 2026

A relatively stable weather pattern prevailed during the morning
hours across Puerto Rico and the U.S. Virgin Islands, with limited
cloud cover and shower activity observed across the region. Maximum
daytime temperatures ranged from the mid-to-upper 80sF and in the
upper 70s to lower 80s across the mountains, resulting in warm
conditions across the local islands, particularly along the coastal
and urban areas of Puerto Rico.

A wetter and more active weather pattern is expected across Puerto
Rico and the U.S. Virgin Islands as tropical moisture gradually
spreads across the region. Model guidance suggests precipitable
water values increasing to around 2.2 to 2.3 inches, well above
climatological normals, while an upper-level trough will provide
additional support for shower and thunderstorm development. At the
surface, a high-pressure system over the central Atlantic will
maintain a southeasterly wind flow across the region, generally
gentle to moderate, with locally fresh winds possible across the
Caribbean waters and southern coastal areas. Under this pattern,
increasing cloudiness may somewhat limit daytime heating; however,
the combination of abundant tropical moisture, local effects, and
sea-breeze convergence will favor scattered to numerous showers and
thunderstorms, particularly across northwestern Puerto Rico during
the afternoon hours, with some activity potentially extending into
the early evening. The main hazards associated with the strongest
showers and thunderstorms will be frequent lightning and periods of
locally heavy rainfall, which may result in minor urban and small-
stream flooding, particularly across low-lying and poor-drainage
areas.

A similar weather pattern is expected to persist across the region,
although some improvement in upper-level conditions is anticipated
as suggested by increasing 250 mb heights. Nevertheless, relatively
cold temperatures at 500 mb, ranging between -7C and -6C, along
with elevated relative humidity values between 850 and 500 mb,
generally near the 75th climatological percentile, will continue to
support an environment favorable for shower and thunderstorm
development. Additionally, upper-level cloudiness may limit daytime
heating, although sufficient moisture and local effects will
continue to support afternoon convection. At the surface, the high-
pressure system over the central Atlantic will gradually expand
toward the Caribbean, promoting a slight shift in the prevailing
winds toward the east-southeast. This wind pattern will favor
passing showers across windward sections during the morning hours,
followed by additional shower and thunderstorm development across
northwestern Puerto Rico during the afternoon. Locally heavy
rainfall and lightning will remain the primary hazards, with minor
flooding possible across urban, low-lying, and poor-drainage areas.

&&

.Long Term(Saturday through Wednesday)...
Issued at 140 AM AST Wed Oct 21 2026

Wet and unsettled weather conditions are expected across Puerto
Rico and the U.S. Virgin Islands on Saturday, followed by gradual
improvement Sunday and a transition toward a drier and more
stable weather pattern early next week.

A southeast to southerly flow, maintained by a deep-layer low
exiting the eastern coast of the United States and surface high
pressure across the central Atlantic, will continue to transport
tropical moisture into the region. Latest GFS guidance indicates
precipitable water values above 2 inches and elevated mid-level
relative humidity through Saturday, supporting scattered to
numerous showers and thunderstorms. Daytime heating, sea-breeze
convergence, and local terrain effects will favor the greatest
convective activity across interior, northern, and western Puerto
Rico. Increasing steering winds should promote more progressive
showers and thunderstorms, although periods of heavy rainfall
remain possible. Some activity may persist into the evening, with
additional showers and thunderstorms developing overnight over the
surrounding waters and coastal areas. The main hazards Saturday
will include frequent lightning, locally heavy rainfall, and gusty
thunderstorm winds. Heavy downpours could lead to ponding of
water on roadways, reduced visibility, urban and small-stream
flooding, and isolated flash flooding, particularly where repeated
showers occur. As rainfall accumulates over several days, the
concern for landslides will also increase, especially in areas of
steep terrain.

By Sunday, a gradual decrease in moisture should result in reduced
shower coverage. However, lingering moisture and local effects
will continue to support afternoon thunderstorms, particularly
across interior and western Puerto Rico. Weakening steering winds
may allow some thunderstorms to move slowly, increasing the
potential for localized rainfall accumulations and isolated
flooding despite the overall improving trend.

A more noticeable improvement is expected Monday through Wednesday
as drier air spreads through the atmospheric column and subsidence
associated with a strengthening mid-level ridge suppresses
widespread convective development. Model guidance continues to
support this transition, with below-normal precipitable water
values and substantially lower mid-level relative humidity.
Although passing showers and isolated afternoon convection will
remain possible, the potential for widespread heavy rainfall and
flooding should decrease considerably.

&&

.AVIATION...
(18Z TAFS)
Issued at 159 PM AST Wed Oct 21 2026

Mainly VFR conds expected across PR and USVI terminals thru the
evening, with only ISOLD SHRA, mainly at TJBQ. VFR conds prevailing
overnight. Increasing moisture will favor more frequent SHRA/VCTS
across terminals aft 22/17Z, with PROB30 TSRA and MVFR/IFR conds at
TJBQ aft 22/21Z. Sfc winds mainly S-SE at 5-12 kt, bcmg L/V
overnight, then 10-14 kt with sea-breeze variations.

&&

.MARINE...
Issued at 159 PM AST Wed Oct 21 2026

Light to gentle south-southeasterly to southeasterly winds will
increase to moderate to locally fresh during the weekend and persist
through at least early next week, resulting in choppy seas. The
current northerly swell will continue to subside, allowing seas to
gradually improve. However, another north-northwesterly swell will
arrive by early Friday, followed by additional pulses through the
weekend. Although seas are expected to remain below Small Craft
Advisory criteria, conditions may require small craft to exercise
caution, particularly across the Atlantic waters and Mona Passage.
Increasing tropical moisture will also favor more frequent showers
and thunderstorms from Thursday through the weekend across the
Caribbean and Atlantic waters and Mona Passage, with lightning,
gusty winds, and reduced visibility.

&&

.BEACH FORECAST...
Issued at 159 PM AST Wed Oct 21 2026

A High Risk of Rip Currents remains in effect through this evening
for north-facing beaches of Puerto Rico, Culebra, St. Thomas, and
St. John. Conditions should briefly improve as the current northerly
swell subsides. However, another north-northwesterly swell arriving
by early Friday, followed by additional pulses through the weekend,
will likely bring a renewed High Risk of Rip Currents to
northwestern and northern exposed beaches, with some potential for
high surf conditions requiring an advisory. Additionally, a wetter
pattern from Thursday through the weekend will increase shower and
thunderstorm activity near coastal areas, resulting in a greater
lightning risk for beachgoers.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk until 6 PM AST this evening for PRZ001-002-
     005-008-010-012.

VI...High Rip Current Risk until 6 PM AST this evening for VIZ001.

AM...None.
&&

$$

SHORT TERM...LIS
AVIATION...CVB/LIS
MARINE/BEACH FORECAST...CVB
LONG TERM....MMC

NWS SJU Office Area Forecast Discussion