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297
FXCA62 TJSJ 271916
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
316 PM AST Mon Apr 27 2026

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

.KEY MESSAGES...
Updated at 309 PM AST Mon Apr 27 2026

* Showers and isolated thunderstorms this afternoon and Tuesday
  will increase flooding and lightning risk, resulting in urban
  and small stream flooding.

* The moderate risk continues over north and east-facing beaches
  Puerto Rico and the U.S. Virgin Islands for the next several
  days. Beachgoers should exercise caution along exposed beaches.

* Warmer-than-normal conditions will continue across urban and
  coastal areas of the islands, with heat indices reaching or
  exceeding 100F, affecting the more vulnerable communities.

* Frequency of showers will increase late tonight into early
  Tuesday across the U.S. Virgin Islands, with ponding of water
  over roadways and poorly drained areas.

&&

.Short Term(This evening through Wednesday)...
Issued at 309 PM AST Mon Apr 27 2026

Afternoon showers and thunderstorms developed over mainly eastern
and interior to northern half of Puerto Rico, prompting several
flood advisories over northern municipalities. Radar estimated
accumulations have reached 2 to 4+ inches over Naranjito, Bayamon,
Toa Alta and Toa Baja where flood advisories have been issued.
While heat index values have dropped significantly in these areas,
southern Puerto Rico and St. Croix continue to report (from
official and unofficial stations) heat indices in the mid-90s to
low 100s. A wetter and more unstable pattern is forecast during
the short term period; satellite derived precipitable water (PWAT)
values indicate a moisture field covering the area with PWAT
values reaching 2.0 to 2.2 inches (above normal values for this
time of the year). This moisture field will continue to stream
over the region from the Caribbean Sea and northern South America
towards the Atlantic, following a shearline well north and east of
the region. Current showers and t-storms over the area will
gradually dissipate and or move offshore, showers will continue to
reach windward sectors of the islands during the overnight hours.
The frequency of showers is forecast to increase late tonight
into early Tuesday the eastern region (including the USVI), with
ponding of water over roadways and poorly drained areas. A
lingering mid- to upper-level trough and reflected surface troughs
will also serve to increase instability. A series of surface
highs and frontal lows moving over the Atlantic will result in
varying surface flow during the period, southeasterly steering
flow today into tomorrow, will become more variable to
northeasterly to then southeasterly late tomorrow into Wednesday
as a col region develops to our north. A limited to elevated risk
of flooding will persist through most of the period, as the above
mentioned pattern supports frequent showers and isolated
thunderstorms each afternoon, particularly over the interior to
northern half of Puerto Rico, as well as downwind of the local
islands (prompting up to a limited flooding risk over Vieques,
Culebra and the USVI). Winds are expected to decrease as the
period continues, prompting slower moving showers and t-storms. At
areas under up to an elevated flooding risk, heavy rainfall can
result in urban and small stream flooding, as well as ponding of
water over roadways and poorly drained areas. There is also a low
chance of flash flooding. 925 mb temperatures will continue at
high end normal to above normal values at coastal areas during the
period prompting a limited heat risk, particularly before
afternoon showers. Low concentrations of saharan dust will also
persist over the region.

&&

.Long Term(Thursday through next Sunday)...
Issued at 304 AM AST Mon Apr 27 2026

As mentioned in previous discussions, a moist and unstable weather
pattern will persist from Thursday through Friday across Puerto Rico
and the U.S. Virgin Islands, accompanied by light to moderate south-
southeasterly winds. This southerly flow will promote warm
temperatures and elevated humidity. Residents and visitors are
encouraged to monitor the forecast, stay well hydrated, take
frequent breaks from the heat, and limit prolonged sun exposure,
particularly during the warmest hours of the day.

From Thursday through Friday, moisture levels will remain above
normal for this time of year, supporting a pattern of daily showers
and isolated thunderstorms. The most active convection is expected
to develop during the afternoon across the interior and northern
portions of Puerto Rico, while morning activity will favor southern
and eastern Puerto Rico as well as the U.S. Virgin Islands. A
gradual drying trend will begin on Saturday, leading to improving
conditions through the weekend. The driest period is expected from
Sunday into Monday, when more stable conditions take hold across the
region. Although afternoon showers may still develop, their coverage
and intensity will decrease. By this time, any shower activity
should be brief and limited.

Warm conditions will persist throughout the period due to the
prevailing south-southeasterly flow. Temperatures at the 925 mb
level will remain above normal through Friday before gradually
easing over the weekend. Maximum surface temperatures will range
from the upper 80s to low 90s across coastal and urban areas, and
from the low to mid 80s in higher elevations. Combined with high
humidity, heat indices are expected to exceed 100 degrees Fahrenheit
daily, especially through Friday with slight moderation by late
weekend.

&&

.AVIATION...
(18Z TAFS)
Issued at 309 PM AST Mon Apr 27 2026

VFR to brief MVFR conditions should prevail. Light to moderate
ESE to SSE flow over the area will steer -SHRA over windward
terminals. However SHRA/TSRA developing over interior PR can
affect TJSJ/TJBQ, and result in brief MVFR/IFR conditions. Lines
of -SHRA/VCSH can also move over southern and eastern (including
USVI) terminals through the period. ESE to SSE flow continues up
to around 12 kts, with higher gusts and sea breeze variations,
becoming light and variable after 27/23z, with land breeze
variations, before increasing again to around 12 kts from the SE
(albeit more variable) after around 28/13Z.

&&

.MARINE...
Issued at 309 PM AST Mon Apr 27 2026

A surface high pressure system over the central Atlantic will
continue to weaken, while a surface low strengthens over the
northwestern Atlantic over the next few days. This weakening
pressure gradient will promote light to gentle southeasterly winds
through at least midweek, becoming more easterly by the latter
part of the week. A surface trough over east of Puerto Rico
combined with an upper-level trough will bring showers and
isolated thunderstorms across the local waters for the rest of
today and tomorrow, Tuesday. Pulses of small, long-period
northeasterly swell will continue to spread across the Atlantic
waters and local passages for the next few days, though seas
should remain between 2 and 4 feet.

&&

.BEACH FORECAST...
Issued at 309 PM AST Mon Apr 27 2026

No changes were made to the beach forecast. Pulses of a small,
long- period northeasterly swell will continue to spread across
local waters and passages, with conditions expected to diminish by
Thursday. Based on the latest nearshore buoy observations near
northern coastal areas of the islands, seas remain between 2 and 3
feet and have a period of 12 - 14 seconds. Taking into account
bathymetry, breaking waves should remain around 5 feet, resulting
in a moderate risk of rip currents along the northern and eastern
beaches of Puerto Rico and the U.S. Virgin Islands. Although the
risk remains low to moderate, beachgoers must exercise caution as
life-threatening rip currents are possible along beaches under
moderate risk. In addition to rip currents, beachgoers should
remain weather alert as afternoon showers and thunderstorms are
expected near northern coastal areas of Puerto Rico, resulting in
heavy rainfall, gusty winds, and lightning.

&&

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

$$

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

NWS SJU Office Area Forecast Discussion