997
FXCA62 TJSJ 280547
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
147 AM AST Mon Sep 28 2026

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

.KEY MESSAGES...
Issued at 113 AM AST Mon Sep 28 2026

- There is a HIGH rip current risk statement out for those
  northern and eastern beaches of PR, as a small northerly swell
  filters across the regional waters. Therefore, tourist and
  visitors are urged to exercise caution and avoid beaches in
  those areas through at least Tuesday morning.

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

- Expect, a limited flooding risk mainly over northwestern PR, due
  to previous rains and additional is forecast to develop aross
  that area today into the end of the workweek.

- Weather conditions are anticipated to change by Friday.
  Therefore, we urge people to continue to monitor our forecast.

&&

.Short Term(Today through Wednesday)...
Issued at 113 AM AST Mon Sep 28 2026

Overnight, generally calm weather conditions prevailed across
the islands, with partly cloudy skies and a few passing showers
mainly affecting eastern and southern Puerto Rico. Rainfall
accumulations remained minimal, with no significant impacts
observed. Winds were mostly from the east-southeast and light.

As mentioned in previous discussions, expect a more seasonal
weather pattern to prevail as model guidances continues to
suggest normal to below- normal precipitable water and dry air at
the mid levels. A few passing showers will filter across the
windward areas of Puerto Rico and the US Virgin Islands during the
morning hours, followed by afternoon showers developing mainly
from the western interior into northwestern Puerto Rico. Streamers
may also produce localized showers downwind from El Yunque and
the smaller islands. Overall, today should offer the most
favorable day of the short- term period, with partly to mostly
sunny skies and limited shower coverage across much of the area.
The heat risk for today remains limited as mostly localized areas
will experience heat near advisory criteria. Where heavier
afternoon showers develop, brief downpours could result in ponding
on roads and in poor drainage areas, but the flooding threat
remains limited.

Strengthening easterly winds will carry patches of trade-wind
moisture across the region, leading to a more variable weather
pattern, particularly on Tuesday. Passing showers will become
more frequent across the US Virgin Islands, eastern and
northeastern Puerto Rico overnight and Tuesday morning. By the
afternoon, local and diurnal effects should promote additional
shower development across the interior and western portions of
Puerto Rico, while streamers could affect areas downwind from El
Yunque and the smaller islands. Tuesday appears to be the most
active day of the short- term period in terms of the potential for
shower frequency and coverage, rather than thunderstorm intensity.
Although isolated thunderstorms remain possible, relatively dry
mid-level air, gradually warming temperatures aloft, and less
favorable lapse rates should limit the depth and organization of
convection. Stronger steering winds should also keep showers
moving, reducing the potential for prolonged rainfall.
Nevertheless, repeated or heavier showers could produce localized
ponding and reduced visibility on roadways, particularly across
eastern Puerto Rico during the morning and western Puerto Rico
during the afternoon.

Wednesday will remain breezy under moderate to locally fresh easterly
trade winds. Periods of passing showers are expected across
windward areas during the overnight and morning hours, followed by
locally induced afternoon showers over western Puerto Rico.
However, warming temperatures aloft and weakening mid-level lapse
rates should increasingly limit the depth and organization of
afternoon convection. Brief heavy rainfall cannot be ruled out,
but showers should generally move quickly, keeping the flooding
threat limited. Gusty winds may accompany the stronger showers,
particularly across exposed coastal locations.

The heat threat during the short term period should be mostly
limited as stronger easterly winds provide better ventilation and
passing clouds and showers offer occasional relief. Nevertheless,
periods of uncomfortable heat remain possible across urban,
coastal, and lower-elevation areas. Residents and visitors
spending extended periods outdoors should continue to stay
hydrated and take breaks from the heat.

&&

.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...
(06Z TAFS)
Issued at 113 AM AST Mon Sep 28 2026

Expect VFR conds thru 28/15Z. Aftn SHRA/TSRA development could
result in brief VCTS at TJBQ/TJPS btw 28/16-23Z. Brief periods of
MVFR psbl across western PR, particularly at TJBQ. E/SE winds
around 6 to 10 kt with higher gusts and sea breeze variations
thru 28/23Z. However, from 29/00Z winds will gradually bcm more E.

&&

.MARINE...
Issued at 113 AM AST Mon Sep 28 2026

A small northerly swell will persist across the
Atlantic waters and passages today 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 and
northern Puerto Rico. Thunderstorms may produce locally higher winds
and seas, lightning, and reduced visibility.

&&

.BEACH FORECAST...
Issued at 113 AM AST Mon Sep 28 2026

The combination of a northerly swell and
strengthening easterly trade winds will bring hazardous beach
conditions beginning this morning and continuing through late
tonight. A High Rip Current Risk will be in effect from northwestern
through northeastern Puerto Rico, including the San Juan metro area,
where life-threatening rip currents are expected. A moderate risk
will continue across other exposed beaches, including western Puerto
Rico, Culebra, Vieques, and the U.S. Virgin Islands. Afternoon
thunderstorms may also pose a lightning threat to beachgoers,
especially across western and northern Puerto Rico, while hot
conditions remain a secondary concern. Conditions should improve
somewhat Tuesday as the swell gradually subsides.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk from 6 AM AST this morning through late
     tonight for PRZ001-002-005-008.

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

$$

SHORT TERM/AVIATION...MMC
LONG TERM...MNG
MARINE/BEACH FORECAST...ICP