512
FXCA62 TJSJ 211739
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
139 PM AST Tue Apr 21 2026

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

.KEY MESSAGES...
Updated at 134 PM AST Tue Apr 21 2026

* Afternoon showers with a few thunderstorms will develop across
  the interior and western PR each day; meanwhile, the USVI can
  expect calm weather with a few showers embedded in the winds.

* Beachgoers can expect a moderate risk of rip currents along
  north- and east-facing beaches throughout the forecast period in
  PR and the USVI. However, a long period northerly swell will
  promote a moderate/high risk on Wednesday as this swell moves
  across the local Atlantic Waters.

* A wetter and more unstable weather pattern will set up over the
  region as early as Thursday afternoon and more likely from
  Friday into early next week.

&&

.Short Term(This evening through Thursday)...
Issued at 134 PM AST Tue Apr 21 2026

In general, we observed calm weather across the USVI and PR in
the morning. However, we detected a few showers moving inland
across the USVI and the eastern third of PR at times. The rest of
the islands had mostly clear skies with no rain. The winds were
mainly from the east-southeast at 10 to 20 mph, with sea-breeze
variations. Maximum temperatures were in the mid- to upper 80s.

This afternoon, showers and a few thunderstorms are expected to
develop across the interior and western Puerto Rico due to local
effects, sea breeze interactions, and diurnal heating. As a
result, the risk of flooding in these areas is limited. Across the
U.S. Virgin Islands, generally calm conditions are expected, with
increasing cloudiness due to low-level advection. Occasional
showers cannot be ruled out tonight and overnight.

A relatively drier air mass will move in tonight and persist
through at least Thursday morning. By Thursday afternoon onward,
an approaching frontal boundary will promote moisture pooling
across the region, increasing shower activity. In terms of
atmospheric stability, the region remains under relatively stable
conditions, driven by zonal flow aloft and a weak mid-level ridge.
These features will begin to erode by Thursday afternoon as a
mid- to upper-level trough amplifies over the western Caribbean,
becoming more pronounced from late Thursday night into Friday. At
the surface, high pressure over the central and eastern Atlantic,
interacting with a frontal boundary over the western Atlantic,
will maintain an east-to-east-southeast wind flow through today,
shifting to east-to-east-northeast on Wednesday and Thursday.

Under this pattern, a typical seasonal weather regime is expected.
Wednesday will feature generally fair weather with passing showers
across windward areas of Puerto Rico and the U.S. Virgin Islands,
followed by afternoon convection over the interior and western
Puerto Rico and downwind of the USVI. Additionally, residents can
expect pleasant overnight temperatures, as mostly clear skies
promote radiational cooling.

&&

.Long Term(Friday through next Monday)...
Issued at 134 PM AST Tue Apr 21 2026

A wetter and more unstable weather pattern is expected to prevail at
the start of the long-term period as remnants of a frontal boundary
linger near the region under southeasterly low-level flow. This
pattern will promote precipitable water values near or above
climatological normals. Afternoon convective development will remain
possible across interior and western/northwestern Puerto Rico, aided
by daytime heating, local effects, and sea breeze convergence. While
widespread rainfall is not anticipated on Friday, moderate rainfall
may still cause localized ponding of water in urban and poorly
drained areas, especially where showers persist or repeatedly affect
the same locations.

Through the weekend, low-level winds are forecast to veer more
southerly, allowing a deeper tropical moisture plume to spread
across the area while also advecting warmer temperatures into the
region. This evolving pattern will likely result in above-normal
daytime temperatures, particularly across coastal and urban areas of
Puerto Rico and the U.S. Virgin Islands. As a result, increased heat
risk is possible during the peak hours of the day, with heat indices
near or slightly above 100 degrees possible in some locations.
Residents and visitors should anticipate warmer and more humid
conditions through the weekend period.

Shower and thunderstorm coverage during the weekend will depend in
part on the availability of mid-level moisture, as the latest
guidance suggests some pockets of drier air aloft may intermittently
limit the overall extent of convection. Nevertheless, sea breeze
convergence, local effects, and stronger daytime heating may still
support isolated to scattered afternoon showers and thunderstorms
each day, with the greatest activity focused over interior and
northern portions of Puerto Rico. Localized urban and small stream
flooding will remain possible where stronger showers develop, along
with brief gusty winds and frequent lightning.

By early next week, a gradual increase in columnar moisture in
combination with some troughiness aloft is expected to support
greater areal coverage of showers and thunderstorms across the
forecast area. This should result in more numerous showers from
Monday into Tuesday, with the greatest afternoon activity once again
focused over interior and western/northwestern portions of Puerto
Rico, while passing showers remain possible elsewhere. In this
pattern, periods of locally heavy rainfall and isolated
thunderstorms will be possible, increasing the potential for urban
flooding, quick river rises, and localized flooding in flood-prone
areas through the latter part of the forecast period.

&&

.AVIATION...
(18Z TAFS)
Issued at 134 PM AST Tue Apr 21 2026

Mainly VFR conds across all TAF sites with VCSH expect over USVI
terminals and JPS through 21/23z. Aftn convc may bring -TSRA over W
PR, with VCTS in JBQ btwn 21/18 - 21/23z. The proximity of the -TSRA
may reduce CIGs/VIS and bring -RA, AMDs will be issued if required.
Winds will weaken aft 21/23z, btwn 5 - 8 kt, while winds will
strengthen btwn 10 - 12 kt, by 22/12 - 22/13z.

&&

.MARINE...
Issued at 134 PM AST Tue Apr 21 2026

A high-pressure system extending from the central to the eastern
Atlantic is interacting with a frontal boundary approaching from
the western Atlantic. This setup will lead to moderate east-to-
east-southeast winds tonight, followed by the return of the trade
winds starting Wednesday. Additionally, long-period swells will
move across the local Atlantic and Caribbean Passages. The first
swell, arriving from the northwest, is expected to arrive around
Wednesday afternoon, followed by a second, larger swell coming
from the north to northeast around Saturday.

&&

.BEACH FORECAST...
Issued at 134 PM AST Tue Apr 21 2026

Beachgoers can expect a moderate risk of rip currents through
much of the forecast period, especially along north- and east-
facing beaches of Puerto Rico and the U.S. Virgin Islands. Looking
ahead, another long-period northerly swell will arrive around
Wednesday afternoon, which could increase the risk to high,
potentially worsening beach conditions.

In addition, beachgoers should remain alert for afternoon
thunderstorms, particularly across western Puerto Rico. These
storms may produce gusty winds and frequent lightning.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

KEY MESSAGES/SHORT TERM/MARINE/BEACH FORECAST...CAM
LONG TERM....CVB
AVIATION...MNG

NWS SJU Office Area Forecast Discussion