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640
FXCA62 TJSJ 281832
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
232 PM AST Mon Sep 28 2026

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

.KEY MESSAGES...
Issued at 217 PM AST Mon Sep 28 2026

- Life-threatening rip currents continue along the north facing
  beaches of Puerto Rico, where a High Rip Current Risk remains in
  effect through late tonight.

- The heat risk for the next few days should be limited, as easterly
  trade winds strengthen, allowing only localized areas across
  Puerto Rico and the US Virgin Islands to experience short periods of
  near heat advisory criteria.

- Passing showers will continue to move at times across the USVI and
  eastern PR, while afternoon thunderstorms develop each day over
  western PR.

&&

.Short Term(This evening through Wednesday)...
Issued at 217 PM AST Mon Sep 28 2026

Fair weather conditions have prevailed over the morning hours, with
a few passing showers across the US Virgin Islands and eastern
Puerto Rico leaving minimal accumulation and a light southeasterly
wind flow. The rest of the day will be dominated by similar fair
conditions. Seasonoal-to-below seasonal precipitable water (PWAT)
values (below 2 inches) will persist through the day along with calm-
to-locally breezy ESE wind flow. Drier mid-to-upper levels will act
to hinder the development of showers and thunderstorms. However, mid-
tropospheric temperatures are still conducive for development of
convective cells. This pattern suggests that any weather that does
develop will be driven by local effects. Thus, passing showers and
streamers from El Yunque and the smaller islands may develop during
the early afternoon hours over the US Virgin Islands and eastern
Puerto Rico. Whereas, showers and thunderstorms may develop across
the interior and western Puerto Rico through the afternoon hours.
Where deep convection and excessive rainfall does occur, there might
be ponding of water in roads and poorly drained areas, along with a
low chance of small streams flooding.

A similar weather pattern is expected for the remainder of the short-
term forecast with seasonal conditions driven by local effects.
Thus, expect to see passing showers develop over the US Virgin
Islands and Puerto Rico during the morning hours and showers and
thunderstorms over the western interior and northwestern Puerto Rico
during the afternoons. Out of all the days in the forecast, Tuesday
promises to be the most active with above average PWAT values
expected across western Puerto Rico during the afternoon. Tuesday is
also forecasted to have a moister column, have locally breezy wind
conditions, and low mid-tropospheric temperatures. These conditions
are favorable for the development of showers and streamers from El
Yunque and the smaller islands. Model guidance suggests that wind
conditions are expected to further strengthen by Wednesday, bringing
more widespread windy conditions to the CWA. They also indicate
drier and warmer mid-levels which will act as a limiting factor for
the development of rainfall activity. Nonetheless, showers and
thunderstorms are still possible given the windy conditions and
local effects.

The short-term period might provide some respite from the high
temperatures that have been observed in the recent periods with
lower low-tropospheric temperatures (around 925 mb) ranging around
normal-to-below normal levels for the season. Thus, the heat risk
for the remainder of the short-term period will remain limited. Heat
risk will predominantly affect exposed and urban areas. While there
is a decreasing trend in temperatures, citizens and visitors are
still urged to remain updated of the changing weather conditions.

&&

.Long Term(Thursday through Monday)...
Issued at 113 AM AST Mon Sep 28 2026

No major changes were introduced to the long-term forecast, with
unstable conditions returning by the end of the week. As mentioned
in the previous discussion, a surface high pressure building over
the Western Atlantic should promote an easterly-southeasterly wind
flow throughout most of the period. Breezy conditions are likely on
Thursday, particularly across coastal areas of the islands, though
winds may weaken by Friday as model guidance suggests a surface
trough interacting with the surface high, strengthening back by
Sunday. In the mid and upper levels, the interaction between the
ridge over the Hispaniola and a TUTT over the Leeward Islands should
bring more stable conditions as the CWA continues under the
subsidence side of the trough on Thursday. Afternoon convection can
still be expected, though showers should be progressive with short-
lived thunderstorms. A transition to a seasonal weather pattern with
unstable conditions is expected by Friday, with abundant tropical
moisture pooled into the region and upper-level troughs near the
area. As mentioned in the previous discussion, the deterministic
guidance of the ECMWF and GFS suggests an increase in PWAT values
most likely to range between 1.8 and 2.0, normal for this time of
year. Taking a look at the cross-section, moisture content in the
low to mid levels should increase to near above climatological
normal (between 60 - 80%), with guidance suggesting skinny sounding
profiles with weak inversion caps. In terms of instability, the
presence of the trough should introduce cooler air in the mid levels
(500 mb temperatures down to -7.5 C) and divergence aloft, favorable
for deeper convection. This pattern should persist on Saturday as
well, improving by Sunday as a drier airmass filters into the region
and limits deep convection. Overall, afternoon convection is
expected each day, particularly across interior and
western/northwestern Puerto Rico, along with the local island
streamers. Windward sections of the islands can expect isolated to
scattered showers during the night and morning hours, though the
eastern side of Puerto Rico could have additional rainfall due to
streamers during the afternoon. Although the weather conditions do
not seem optimal for flooding, ponding of water over roadways and
poorly drained areas can be expected on Thursday. On the other hand,
the flooding threat should increase on Friday and Saturday, with
urban and small stream likely across the aforementioned areas,
without ruling out the San Juan Metro Area.  For the moment, the
flooding threat should remain low on Sunday. In addition to
flooding, thunderstorm activity could produce gusty winds and
frequent lightning.

As mentioned in the previous discussion, seasonal to warmer
conditions are still on forecast, with above climatological normal
925 mb temperatures during the second part of the workweek. Although
afternoon convection may start earlier, temperatures may rise
quickly during the morning hours, with heat indices exceeding 100 F
across urban and low-lying areas. Therefore, the heat threat will
remain limited to elevated throughout the forecast period.

&&

.AVIATION...
(18Z TAFS)
Issued at 217 PM AST Mon Sep 28 2026

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, passing SHRA may cause tempo MVFR
conds at TIST thru 28/21z. Elsewhere, mostly VCSH expected. The
28/12z TJSJ sounding indicated east winds up to 17 kt blo FL030.
Light and variable winds expected overnight, increasing from the
ENE at 12-16 kt with higher gusts aft 29/13z.

&&

.MARINE...
Issued at 217 PM AST Mon Sep 28 2026

A small northerly swell will persist across the Atlantic waters and
passages through tonight as moderate easterly trade winds gradually
strengthen. Choppy conditions will continue across the Atlantic
waters and Mona Passage, with locally fresh winds expected by
Tuesday night into Wednesday. Periods of showers will remain
possible across the local waters, with the more typical afternoon
activity and isolated thunderstorms expected near western Puerto
Rico. Thunderstorms may produce locally higher winds and seas,
lightning, and reduced visibility at times.

&&

.BEACH FORECAST...
Issued at 217 PM AST Mon Sep 28 2026

A northerly swell will maintain a high rip current risk through at
least late tonight from northwestern through northeastern Puerto
Rico, including the San Juan metro area, where life-threatening rip
currents are expected. Therefore, a Rip Current Statement is in
effect for those areas, and beachgoers are urged to avoid those
beaches as dangerous rip currents are expected. Moderate rip current
risk continue in the western beaches of Puerto Rico, as well as
Vieques, Culebra and the U.S. Virgin Islands.

The moderate risk will continue along the northern, eastern and
western beaches, including Vieques, Culebra and the U.S. Virgin
Islands due to strengthening easterly trade winds. This means
that rip currents are possible in the surf zone.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through late tonight for PRZ001-002-005-
     008.

VI...None.
AM...None.
&&

$$

SHORT TERM/KEY MESSAGES...RVM
LONG TERM....MNG
AVIATION...DSR
MARINE/BEACH FORECAST...KML

NWS SJU Office Area Forecast Discussion