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339
FXCA62 TJSJ 051840
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
240 PM AST Wed Aug 5 2026

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

.KEY MESSAGES...
Issued at 235 PM AST Wed Aug 5 2026

- Hot and hazardous conditions will remain the primary weather
  concern through the remainder of the week and into the weekend.
  Heat Advisories continue through 5 PM AST this afternoon across
  Puerto Rico and the U.S. Virgin Islands, and additional heat
  products will likely be needed in the coming days as above-
  normal temperatures and dangerous heat indices persist.

- Passing showers and isolated thunderstorms will continue this
  afternoon, mainly across the interior and northwestern sections
  of Puerto Rico.

- A more stable air mass will settle over the region tomorrow
  into the weekend, bringing fewer showers and increasing
  concentrations of Saharan dust.

- Elevated fire weather conditions may develop tomorrow into the
  weekend. Lower relative humidity, drying fuels, and breezy east
  to east-southeast winds could increase the potential for rapid
  wildfire spread, particularly across areas with dry vegetation.
  Residents should avoid outdoor burning and exercise caution with
  activities that could produce sparks.

&&

.Short Term(This evening through Friday)...
Issued at 235 PM AST Wed Aug 5 2026

Variable conditions persisted in the morning hours as a surface
trough moved north of the CWA, bringing isolated to scattered
showers and thunderstorms across the regional waters. Although
isolated showers moved across portions of eastern Puerto Rico and
the U.S. Virgin Islands, the WSR-88D rainfall estimation remained
low. Minimum temperatures were slightly cooler than yesterday, with
ASOS/AWOS stations reporting mid to upper 70s (so far, maximum
temperature at the LMM airport is 92 degrees Fahrenheit), as well as
stations across the islands` coastal areas. Meanwhile, higher
elevations remained in the low to mid 60s. Temperatures continued to
increase during the morning hours, reaching the upper 80s and low
90s across urban and low-lying areas, with heat indices exceeding
100 degrees Fahrenheit. The Heat Advisory remains in effect through
5 PM AST. The 12z RAOB reflected a more skinny profile in the low
to mid levels, with PWAT values reaching 2 inches (yesterday: 1.76
inches. This change is reflected in the mid-levels, with less
presence of Saharan Dust and the proximity of a surface trough,
located north of the CWA. At around 15z, convection activity began
for portions of interior and northwestern Puerto Rico, including
local streamers. Based on the latest HIRES models, showers and
isolated thunderstorms should continue in the afternoon, with the
best chance of flooding over portions of northwestern Puerto Rico.
Rainfall accumulations could lead to ponding of water over roadways
and poorly drained areas.

The short-term forecast remains on track. Wind pattern will mostly
prevail from the E-SE, becoming from the E-NE by Friday as a surface
high pressure builds over the western Atlantic. The latest satellite-
derived images show an area of drier and more stable airmass
filtering into the region. From the latest model guidance, PWAT
values should gradually drop to below climatological normal (1.2 -
1.4 inches), as low to mid level moisture content plummets as well
(700 - 500 mb RH below 30 - 40 %). Additionally, an upper-level low
over the Hispaniola moves westward, the influence of a mid level
ridge should warm mid-level temperatures (between -5 and
-6 degrees Celsius), bringing subsidence and promoting stability
aloft. Hence, shower activity should become less frequent, with the
most likely scenario being few isolated showers moving tonight into
the morning hours over windward sections, followed by afternoon
convection. The combination of daytime heating, local effects, and
sea breeze convergence should favor convection activity over
interior and northwestern Puerto Rico, though rainfall accumulations
will likely remain localized, with a low flood threat. A similar
pattern could repeat on Friday, with showers becoming more
progressive as the surface high pressure and winds strengthen.
Nevertheless, no flood nor lightning threat is expected.

As mentioned in the previous discussion, heat remains as the main
threat in the short-term, as warmer to hot conditions will likely
continue according to model guidance. Combined with the available
moisture, heat indices will easily exceed 100 degrees Fahrenheit,
particularly over urban and lower elevations of the islands. Hence,
h eat products will likely be issued, without ruling out an Extreme
Heat Warning.

&&

.Long Term(Saturday through Wednesday)...
Issued at 142 AM AST Wed Aug 5 2026

A drying trend is expected for most of the long-term period as a
strengthening, broad surface high-pressure system extending across
the western and central Atlantic dominates local weather conditions.
Under this pattern, an east-to-southeast wind flow will prevail
through Monday, turning east-northeasterly from Tuesday onward.

An upper-level low-pressure system moving across the region from
Saturday into Monday will provide slight instability aloft,
reflected in cooler 500 mb temperatures dropping to between -6C and
-7C. However, despite this atmospheric setup, overall drier
conditions are expected, though patches of low-level moisture
carried by the trade winds will move across the region from time to
time. During this period passing showers will affect eastern Puerto
Rico and the U.S. Virgin Islands during the morning hours. Followed
in the afternoon, available moisture combined with diurnal heating
and local sea-breeze effects could trigger localized convective
activity across central and western Puerto Rico.

Warmer-than-normal temperatures will persist throughout the forecast
period. Model guidance indicates 925 mb temperatures near two
standard deviations above normal for this time of year, which,
combined with lingering moisture, could result in Heat Advisories or
Extreme Heat Warnings, particularly on Monday.

&&

.AVIATION...
(18Z TAFS)
Issued at 235 PM AST Wed Aug 5 2026

Mainly VFR conds should persist across TAF sites, with TEMPO over
JBQ as CIGs/VIS may drop and lead to MVFR conds due to -TSRA in NW
PR through at least 05/20z, while VCSH may persist across most
terminals aft 05/23z. Winds from the E-SE may weaken and become VRB
tonight, strengthening btwn 10 - 15 kt with brf gusts aft 06/12-13z.
VCTS is expected once again at JBQ by 06/17z.

&&

.MARINE...
Issued at 235 PM AST Wed Aug 5 2026

Marine conditions remain generally favorable across the regional
waters tonight, with seas of 2 to 4 feet and east to east-
southeasterly winds of 10 to 15 knots. Isolated thunderstorms over
western Puerto Rico may produce locally higher winds, rough seas,
and frequent lightning through the late afternoon. A strengthening
surface high over the western Atlantic will promote increasing
easterly winds from Thursday into the weekend, resulting in choppier
seas, particularly across the offshore Atlantic waters and local
passages. Moderate concentrations of Saharan dust are expected to
return late Friday and persist through the weekend, reducing
visibility at times.

&&

.BEACH FORECAST...
Issued at 235 PM AST Wed Aug 5 2026

A low risk of life-threatening rip currents will continue tonight
for most local beaches. As easterly winds strengthen late Thursday,
a moderate risk of rip currents is expected to develop along the
north- and east-facing beaches of Puerto Rico, Vieques, Culebra, and
the U.S. Virgin Islands, continuing into the weekend.

Heat remains the primary beach hazard through the remainder of the
week and into the weekend, with above-normal temperatures and
elevated heat indices expected each day. Beachgoers are encouraged
to stay hydrated, seek shade frequently, and limit prolonged sun
exposure during the afternoon hours. Isolated thunderstorms this
afternoon may produce locally hazardous conditions across the
northwestern coastal waters and beaches of Puerto Rico before a more
stable weather pattern develops for the latter part of the week.
Moderate Saharan dust concentrations are expected to return late
Friday into the weekend, occasionally reducing visibility.

&&

.FIRE WEATHER...
Issued at 235 PM AST Wed Aug 5 2026

Critically dry fuels continue across portions of the local islands,
particularly across southern Puerto Rico, St. Croix, and other fire-
prone areas of the U.S. Virgin Islands. Although isolated showers
and localized thunderstorms remain possible this afternoon, mainly
across interior and western Puerto Rico, recent rainfall has been
limited over the southern coastal plains, where fuels remain
receptive to fire starts. Winds will remain relatively light today,
keeping the fire weather threat limited through the remainder of the
afternoon.

A drier and more stable weather pattern will become established
beginning Thursday and persist into the weekend as moisture
decreases and easterly winds strengthen. Lower relative humidity,
increasing sunshine, and breezy conditions, combined with critically
dry fuels, will elevate the potential for rapid wildfire growth and
spread, particularly across southern Puerto Rico and the U.S. Virgin
Islands. Residents and visitors are encouraged to avoid outdoor
burning and use caution with activities that could produce sparks,
as fire weather conditions are expected to become increasingly
favorable in the coming days.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007-
     008-010>013.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...None.
&&

$$

SHORT TERM/AVIATION...MNG
LONG TERM...GRS
MARINE/BEACH/FIRE...CVB

NWS SJU Office Area Forecast Discussion