759
FXCA62 TJSJ 240720
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
320 AM AST Mon Aug 24 2026

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

.KEY MESSAGES...
Issued at 320 AM AST Mon Aug 24 2026

 * A Heat Advisory is in effect today from 10 AM to 4 PM AST, as
   warm temperatures and elevated heat indices are expected to
   result in hazardous heat conditions, particularly across
   coastal and urban areas during the late morning and afternoon
   hours.

 * A drier air mass is expected today, limiting widespread shower
   activity across the region. However, moisture will increase
   late tonight into Tuesday as a tropical wave approaches the
   islands, increasing the potential for showers across the
   region.

 * Saharan dust particles in moderate concentrations are expected
   across the islands from Wednesday afternoon into Thursday,
   resulting in hazy skies and limited shower activity.

 * A low risk of rip currents is expected today, increasing to
   moderate by Thursday.

 &&

.Short Term(Today through Wednesday)...
Issued at 320 AM AST Mon Aug 24 2026

A variable weather pattern was observed during the overnight
hours, with isolated to  scattered showers moving across eastern
sections of Puerto Rico. The most significant shower activity was
observed along the eastern coastal municipalities, where rainfall
accumulations reached nearly 0.75 inches across portions of
Naguabo. As of 1 AM, the showers had moved inland from the coast
and spread into the vicinity of Caguas, gradually diminishing
across these areas. Additional showers were also observed over the
local Atlantic waters. Overnight temperatures were in the lower
80s across coastal and urban areas of northern Puerto Rico, while
unofficial stations across eastern Puerto Rico reported minimum
temperatures in the mid to upper 70s. Similar overnight
temperatures were observed across the mountainous areas, with a
few isolated areas in the higher elevations reporting temperatures
in the upper 60s.

The weather pattern for the rest of the morning and into the
afternoon hours will be mostly driven by a surface high pressure
over the western Atlantic in combination with a surface low
pressure over the central Atlantic, which will continue to promote
an east to east-southeasterly wind flow across the region. Under
this pattern, passing showers across the local waters and portions
of the islands will continue during the early morning hours as the
moisture field associated with the previous weak tropical wave
continues to move out of the region. A slightly drier air mass,
currently located just east of the U.S. Virgin Islands and
accompanied by low concentrations of Saharan dust, will gradually
move into the area later this morning. Therefore, drier conditions
with more limited shower activity are expected. Increasing periods
of sunshine will also enhance warm temperatures and heat indices
across coastal and urban areas, which could exacerbate the heat
threat, particularly for vulnerable populations. Therefore a heat
advisory is in effect for those areas from 10 AM to 4 PM AST.
Conditions will not be completely dry across the islands, as local
effects are expected to result in afternoon showers across
northwestern Puerto Rico, where the strongest activity could
result in minor ponding of water across poor-drainage areas. Since
the mid-level ridge will continue to provide relatively stable
conditions, along with warmer temperatures at 500 mb, widespread
convective activity will remain limited. However, an isolated
thunderstorm or two will remain possible with the strongest
afternoon showers.

By Tuesday, a similar surface pattern in terms of the synoptic
features will remain in place. However, the surface high pressure
will extend into the central Atlantic, maintaining a more
southeasterly wind flow. Under this pattern, another tropical wave
(a more defined one compared to the previous wave) is forecast to
move over the CWA. This will increase PWAT values to around the
75th percentile in climo values, along with an increase in 850-500
mb relative humidity. So far today, Tuesday looks like the best
day for more widespread shower activity, with additional rainfall
expected across eastern and interior sections , as well as western
Puerto Rico during the afternoon hours. Although an increase in
rainfall activity is expected, forecast rainfall accumulations
will likely not be enough to significantly improve the ongoing
drought conditions across the affected areas. By Wednesday,
surface and low-level high pressure centered over the western
Atlantic will continue to expand into the central Atlantic,
causing winds to shift back to a more easterly direction across
the region. Under this easterly wind regime, a more typical
summertime weather pattern is expected across the islands, with
afternoon convection mainly driven by local and sea breeze
effects. At the same time, the NASA Goddard Earth Observing System
Model V5 suggests an increase in Saharan dust particles across the
region, with moderate concentrations expected to filter into the
islands.

&&

.Long Term(Thursday through Monday)...
Issued at 320 AM AST Mon Aug 24 2026

A surface high pressure system over the central
Atlantic will dominate local weather conditions through much of the
period, driving mostly east-southeasterly winds across the
northeastern Caribbean. A mid-level ridge aloft will further
reinforce dry, stable air.

Drier-than-normal conditions are expected to prevail Thursday and
Friday, with precipitable water (PWAT) values remaining below the
climatological normal of 1.25 inches. Nevertheless, passing patches
of moisture will bring brief, fast-moving showers to the region.
Afternoon convection driven by daytime heating and localized effects
may trigger showers and a few isolated thunderstorms over western
Puerto Rico.

From Friday night into Saturday, the latest model guidance suggests
a tropical wave will approach the area. However, the bulk of its
moisture is expected to remain over the Caribbean Sea, with only the
northern periphery reaching the region to bring PWAT values up to
1.751.90 inches. Because some uncertainty remains, residents and
local interests should continue monitoring forecast updates as this
wave evolves.

PWAT values will drop rapidly following the wave`s passage, re-
establishing dry, stable air and limiting rainfall chances through
early next week. Meanwhile, warmer-than-normal temperatures will
persist throughout the forecast period. Model guidance shows 925 mb
temperatures running nearly two standard deviations above average
for this time of year. Combined with southeasterly winds, seasonal
moisture, and Saharan dust, these conditions may warrant heat
advisories or warnings by the end of the week.


&&

.AVIATION...
(06Z TAFS)
Issued at 320 AM AST Mon Aug 24 2026

VFR conds are expected to prevail across all terminals through the
period. Passing SHRA will remain possible across TJSJ/TIST/TISX
during the morning hours. A slightly drier air mass will filter
into the region later this morning. Afternoon SHRA are expected to
develop across interior and NW PR after 24/16Z. VCTS are possible
near TJBQ, with brief MVFR conds. E-ESE winds at 10-15 kt will
prevail, with locally higher gusts. SHRA are forecast to increase
by the end of the period along well east TAF sites.

&&

.MARINE...
Issued at 320 AM AST Mon Aug 24 2026

A surface high pressure over the western Atlantic in combination
with a low pressure system across the central Atlantic will
continue to hold moderate east-southeasterly winds across the
area. Under this pattern seas will generally remain between 3 to
5 feet across most of the local waters for the day. For the rest
of the morning, some showers with isolated thunderstorms might
continue to affect the western offshore Atlantic waters. A
tropical wave is forecast to approach the eastern Caribbean around
Tuesday, bringing enhanced shower and thunderstorm activity over
the waters. Winds will gradually increase by midweek, becoming
moderate to locally fresh, seas should build to 3-5 feet,
occasionally 6 feet, across offshore waters and passages. Small
craft must exercise caution during that time.

&&

.BEACH FORECAST...
Issued at 320 AM AST Mon Aug 24 2026

Beach conditions remain tranquil for beachgoers, as the low risk of
rip currents continues across the islands. These conditions should
continue for the first part of the week, though beachgoers must
exercise caution, as life-threatening rip currents can often occur
in the vicinity of jetties, reefs, groins, and piers. By midweek, a
gradual increase in winds and seas will likely upgrade the risk to
moderate, particularly on Thursday across northern and eastern-
exposed beaches of the islands, increasing the likelihood of rip
currents along the surf zone. The moderate risk should continue
throughout the end of the week. As mentioned in the previous
discussion, showers and isolated thunderstorms can be expected each
afternoon, moving across western coastal areas of Puerto Rico.
Beachgoers should remain weather alert, as isolated thunderstorms
could produce gusty winds and lightning.

&&

.FIRE WEATHER...
Issued at 320 AM AST Mon Aug 24 2026

The available of moisture during the morning hours will induce
the RH values remain in the low 60s across most of the region. By
afternoon hours as a more drier airmass moves into the region, RH
values could briefly drop and reach the fire danger threat for
some souther coastal areas but not widespread. In term of
surface winds, a more east-southeasterly wind pattern is forecast
aiding some Caribbean factor to the equation. The constant value
for fire danger criteria is the soils conditions across most of
the affected area. However, giving the expected conditions in the
variable conditions, the risk of fire danger threat will remain
moderate today.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon
     for PRZ001>003-005-007-008-010>013.

VI...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon
     for VIZ001-002.

AM...None.
&&

$$

SHORT TERM,AVIAITON & KEY MESSAGES...LIS
LONG TERM....GRS
MARINE & BEACH FORECAST...MMC