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702
FXCA62 TJSJ 201900
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
300 PM AST Thu Aug 20 2026

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

.KEY MESSAGES...
Issued at 300 PM AST Thu Aug 20 2026

- A drier airmass with Saharan dust particles will dominate the local
  region the rest of today and Friday, with limited afternoon
  showers expected across western Puerto Rico. During the weekend,
  patches of moisture may increase slightly the frequency of
  passing showers and afternoon convection across western Puerto
  Rico.

- A Heat Advisory remains in effect until this afternoon across urban
  and coastal areas of the islands. The heat will likely continue
  to be a threat in the coming days.

- A moderate risk of rip currents will return tonight into Friday along
  the beaches of northern and eastern Puerto Rico, Culebra,
  Vieques, and the U.S. Virgin Islands.

- A Fire Danger Statement (RFD) remains in effect until 5 PM AST this
  afternoon, particularly across the southern plains and hills of
  Puerto Rico due to minimum relative humidity values in the mid
  50s and easterly winds near 15 mph and higher gusts.

&&

.Short Term(This evening through Saturday)...
Issued at 300 PM AST Thu Aug 20 2026

A generally hot, dry and hazy day was experienced across the
islands, as a dry air mass with below normal precipitable water
(PWAT) values and moderate to high Saharan Dust concentrations have
moved over the region. Although an upper-level low is lingering
north of the islands and a tropical wave is moving well south, mid-
level ridging and the above mentioned dry air with Saharan Dust has
served to inhibit shower activity and limit available moisture to
the lower levels. The latest local sounding has served to further
evidence this as it reported a strong 800 to 850mb inversion along
with PWAT values at 1.31 inches. Current Satellite derived PWAT
values also indicate values ranging from around 1 to 1.33 inches,
with the exception of NW PR where afternoon convection has resulted
in up to 1.7 in of PWAT. These convective showers and isolated t-
storms have developed due to the up to breezy ESE flow, orographic
effects and sea breeze convergence.

Breezy steering flow during the next few days will be generally
easterly to east-southeasterly during the period and gradually
decrease on Saturday. This flow could steer passing showers over
windward sectors tonight as afternoon convection sharply dissipates
this afternoon. The upper level low will gradually move north and
away from the region as the week continues. Patches of moisture
advecting over the region will become more frequent as the short
term period progresses. This will sustain more seasonal PWAT values,
passing showers during the overnight and morning, and afternoon
convective showers and isolated t-storms over mainly western PR.
Saharan Dust concentrations will gradually decrease as the period
continues with current guidance suggesting low to locally moderate
concentrations on Saturday. This activity should be more notable on
Saturday as available moisture, decreased dust concentrations,
diurnal heating, sea breeze convergence and local effects can result
in a limited flooding risk over western Puerto Rico. Dry mid levels
with Saharan dust concentrations will continue to limit shower
activity and keep available moisture in the low levels. Temperatures
have reached the 90s while heat indices have reached the mid to
upper 100s to the low 110s across urban and coastal sectors of the
islands. A Heat Advisory will continue for these areas through 5 PM
AST; heat risks are expected each late morning to afternoon during
the period. Residents and visitors should take necessary precautions
and monitor for additional heat products during the period as both
low and high temperatures remain seasonal to above seasonal.

&&

.Long Term(Sunday through Thursday)...
Issued at 245 AM AST Thu Aug 20 2026

Moisture is expected to increase Sunday into Monday as a tropical
wave approaches the region. The latest model guidance suggests
precipitable water and lower to mid level relative humidity
increasing to near or above normal values for this time of year,
particularly by Monday. This should favor an increase in passing
showers and localized afternoon convection, with locally heavy
rainfall possible. As a result, the main hazards Sunday into Monday
will be lightning and localized flooding, especially where repeated
or heavier showers and thunderstorms occur.

A drying trend is then expected behind the wave Tuesday into
midweek. Although low-level moisture may linger, mid-level relative
humidity decreases considerably through Wednesday as heights rise
and temperatures aloft gradually warm. This should increasingly
limit the vertical depth and coverage of convection and reduce the
potential for significant rainfall. With fewer showers and greater
periods of sunshine, heat will become the primary hazard from
Tuesday into midweek, with elevated to locally significant heat risk
possible during the afternoon hours.

Overall, the primary hazards transition from localized flooding and
lightning Sunday into Monday to increasing heat concerns Tuesday
through midweek.

&&

.AVIATION...
(18Z TAFS)
Issued at 300 PM AST Thu Aug 20 2026

VFR conditions will prevail, with a Saharan Air Layer resulting in
local reductions in visibilities and HZ. VCSH/very brief VCTS
possible near TJBQ. Passing VCSH can move over the eastern region
late tonight. E to ESE flow decreasing to 5 to 10 kts after 21/23Z,
and increasing again to 21/13z to around 14 to 20 kts with higher
gusts.

&&

.MARINE...
Issued at 300 PM AST Thu Aug 20 2026

Moderate to locally fresh easterly winds will continue the rest of
today into tonight, maintaining locally choppy conditions across
portions of the offshore waters and local passages, where Small
Craft should exercise caution. Seas 4 to 5 feet, occasionally to 6
feet across offshore waters while 3 to 4 across coastal waters.
Winds will gradually subside Friday into the weekend, though
occasionally breezy conditions may persist across the more exposed
waters.

&&

.BEACH FORECAST...
Issued at 300 PM AST Thu Aug 20 2026

Tonight into Friday, there is a moderate risk of rip currents along
the beaches of northern and eastern Puerto Rico, Culebra, Vieques,
and the U.S. Virgin Islands, meaning life-threatening rip currents
are possible. A generally lower risk will prevail elsewhere.
However, remember that even when the risk is low, life-threatening
rip currents can occur near groins, jetties, reefs, and piers.

By the weekend into early next week, with slightly lighter winds,
the risk is forecast to fluctuate between low and moderate across
exposed beaches. From Tuesday into midweek, winds are expected to
gradually become breezier, with a moderate risk expanding to most
local beaches. Additional hazards will include heat across all areas
and isolated thunderstorms, particularly across the western beaches
of Puerto Rico during the afternoons.

&&

.FIRE WEATHER...
Issued at 300 PM AST Thu Aug 20 2026

Surface weather stations have been recording minimum relative
humidity values in the mid 50s and easterly winds near 15 mph, with
gusts up to 25 to 28 mph, particularly across the southern plains
and hills of Puerto Rico and St. Croix. An elevated fire danger
threat prevails in these areas due to a combination of dry
atmospheric conditions, ongoing rainfall deficits, stressed
vegetation, and dry fuels. Conditions will remain favorable for
rapid fire ignition and spread. Therefore, a Fire Danger Statement
(RFD) remains in effect until 5 PM AST this afternoon, particularly
across the southern plains and hills of Puerto Rico. Continue to
monitor the forecast, as additional fire weather products may be
needed 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...MRR
LONG TERM....MMC
KEY MESSAGES/MARINE/BEACH FORECAST...YZR

NWS SJU Office Area Forecast Discussion