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478
FXCA62 TJSJ 271813
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
213 PM AST Thu Aug 27 2026

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

.KEY MESSAGES...
Updated at 157 PM AST Thu Aug 27 2026

- Extreme Heat Primary Threat: Extreme heat remains the main hazard,
  especially across urban and coastal areas.

- Variable Moisture Pattern: Intermittent moisture patches will alternate
  with below-normal moisture during drier periods through
  Saturday.

- Active Afternoons: Afternoon showers and thunderstorms will
  remain active across portions of Puerto Rico, with locally
  heavy rainfall possible.

- Watching Dolly Sunday to Monday: Dolly is expected to weaken
  while approaching the northeastern Caribbean. Associated
  moisture may increase showers and thunderstorms, but impacts
  remain uncertain.

- Marine and Coastal Hazards Increase: Marine conditions and rip-
  current risks are expected to worsen late this weekend into
  early next week.

&&

.Short Term(This evening through Saturday)...
Issued at 157 PM AST Thu Aug 27 2026

A drier and more stable air mass will spread across the region
tonight as today`s moisture moves west. Strengthening mid-level
ridging and increasing subsidence will reinforce the trade-wind
inversion, limiting shower development. Nevertheless, patches of low-
level moisture embedded in the easterly flow will continue to
support brief passing showers across windward areas overnight.

A variable moisture pattern will continue Friday into Saturday, with
intermittent patches of moisture alternating with periods of below-
normal moisture. Friday should feature the driest conditions,
although passing morning showers and locally induced afternoon
convection will remain possible. Shower and thunderstorm activity
should become somewhat more active Saturday as an easterly
disturbance and increasing moisture move across the region.
Afternoon convection will favor the interior and western portions of
Puerto Rico, where locally heavy downpours could result in ponding
of water and localized flooding.

Extreme heat remains the primary hazard through the short-term
period. Heat risk should decrease closer to normal levels Friday,
before increasing above normal again Saturday. The highest heat
impacts will continue to favor urban and coastal areas, particularly
during periods of reduced cloud and shower coverage.

Mainly VFR thru the period. SHRA near PR terminals thru this
evening, improving overnight. Aftn SHRA/iso TSRA mainly interior/wrn
PR may cause brief MVFR and mtn obsc, especially near TJBQ. E winds
15-20 kt with higher gusts/sea-breeze variations, decreasing to 5-10
kt and VRB aft 27/23Z.

&&

.Long Term(Sunday through next Wednesday)...
Issued at 157 PM AST Thu Aug 27 2026

Forecast uncertainty remains higher than usual heading into early
next week, primarily associated with Tropical Storm Dolly, currently
over the central tropical Atlantic. According to the latest Tropical
Weather Outlook from the National Hurricane Center, the storm has
become favorable for cyclonic development, though the system will
likely remain short-lived as environmental conditions are expected
to become less conducive for development this weekend. Nevertheless,
the evolution of Dolly and its associated moisture field will
continue to be monitored for potential impacts across Puerto Rico
and the U.S. Virgin Islands.

The current forecast generally follows the timing depicted by the
GFS and ECMWF, both of which indicate increasing moisture and
precipitable water values from late Sunday through at least Tuesday.
Although their timing is relatively similar, the GFS remains more
aggressive with moisture and rainfall than the ECMWF.
Part of this difference appears related to the evolution of the mid-
level ridge. The ECMWF maintains stronger ridging closer to the
northeastern Caribbean Sunday into Monday, which would favor greater
subsidence and potentially disrupt the disturbance and its moisture
field. In contrast, the GFS shifts the ridge farther west ahead of
Dolly, allowing deeper moisture to approach the region.

Given these trends, the forecast favors a wetter pattern Sunday into
Monday, with increasing shower and thunderstorm activity and a more
widespread limited flooding risk. Steering flow should favor passing
showers across windward areas, followed by afternoon convection
mainly across the interior and western to northwestern portions of
Puerto Rico. Locally heavier rainfall will ultimately depend on the
track and structure of Dolly and the distribution of its associated
moisture.

Moisture should gradually decrease by late Tuesday as guidance
indicates low to moderate concentrations of Saharan dust reaching
the region. Nevertheless, precipitable water values are forecast to
remain near the upper end of climatological values or above normal
through much of the remainder of the period. Lingering moisture
associated with Dolly, followed by another tropical wave passing
mainly south of the islands Wednesday night into Thursday, should
maintain periods of passing showers across windward areas and
afternoon convection over Puerto Rico under persistent east-
southeast flow.

Meanwhile, seasonal to above-seasonal 925-mb temperatures are
expected to persist, maintaining the potential for elevated to
significant heat impacts, particularly during periods of reduced
cloud cover and rainfall. Given the uncertainty surrounding Dolly,
continue to monitor the latest Tropical Weather Outlook from the
National Hurricane Center and subsequent forecasts from NWS San Juan
for changes in its evolution and potential impacts.

&&

.AVIATION...
(18Z TAFS)
Issued at 157 PM AST Thu Aug 27 2026

VFR condt across most TAF sites, with brief MVFR condt in the
vicinity of TJBQ and TJPS. SE winds around 6 to 16 kts gradually
diminishing after 28/23Z. Tropical Storm Dolly has develop and
could potentially reach the islands by Sunday.

&&

.MARINE...
Issued at 157 PM AST Thu Aug 27 2026

Tropical Storm Dolly has formed and is expected to reach the local
waters from late Sunday into early next week. Winds may briefly
become moderate to locally fresh as the system moves across the
area, with seas between 5 and 7 feet, occasionally 9 feet across the
Offshore Atlantic waters. Small Craft Advisory possible. Surface
high pressure across the central Atlantic will promote a moderate
east to east-southeast wind flow through the weekend. Expect the
first round of increasing showers and isolated thunderstorms by
Saturday.

&&

.BEACH FORECAST...
Issued at 157 PM AST Thu Aug 27 2026

A moderate risk of rip currents will continue along the northern and
eastern exposed beaches of Puerto Rico and the U.S. Virgin Islands
during the next several days. Beachgoers must exercise caution, as
life-threatening rip currents are possible along the surf zone.
Beachgoers are urged to remain weather alert regarding the
development of Tropical Storm Dolly.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>003-005-
     007-008-010>013.

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

AM...None.
&&

$$

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

NWS SJU Office Area Forecast Discussion