261
FXCA62 TJSJ 280931
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
531 AM AST Thu Aug 28 2025

.KEY MESSAGES...

* A tropical wave will continue to approach the islands increase
  the moisture content through Friday.

* An Extreme Heat Warning will be in effect from 10 AM through 5
  PM for the coastal and urban areas of Puerto Rico.

* A Heat Advisory will be in effect from 10 AM through 5 PM for
  the US Virgin Islands, Vieques, and Culebra.

* Seas will continue to subside across the regional waters during
  the next few days, and a low risk of rip currents is expected
  during the weekend across all beaches of PR and the USVI.


&&

.SHORT TERM...Today through Saturday...

Radar estimated accumulations since midnight were observed over
eastern, eastern interior to north-central and southern Puerto Rico,
eastern Vieques, St. Croix and St. John. By 4:32 AM AST, the highest
radar estimated accumulations were 1.47 in over coastal Salinas and
around 1.20 in over Fajardo, Luquillo and Las Piedras. Around 0.01
inches was estimated by radar since midnight at isolated sectors of
St. John and St. Croix. Reported lows were in the mid 60s to low 70s
over interior Puerto Rico, and in the upper 70s to low 80s over
lower elevations of the islands.

Satellite derived precipitable water (PWAT) values indicate a patch
of moisture over the Atlantic Waters with values around 1.90 inches.
Moisture over the Caribbean waters from a weak tropical wave is also
present, with PWAT values around 1.90 to 2 in. Under southeasterly
steering flow, this moisture, along with showers and t-storms will
filter into our local area to start the morning hours. Steering flow
will gradually back to become more east-southeasterly during the
overnight hours into tomorrow, and possibly become more easterly on
Saturday. An elevated to significant heat risk will be present
today, prompting the issuance of a Heat Advisory (USVI, Vieques and
Culebra) and Excessive Heat Warning (lower elevation and urban areas
of PR) from 10 AM to 5 PM AST. 925 mb temperatures are expected to
be above normal (2 standard deviations) for this time of the year.
This diurnal heating, along with orographic effects, southeasterly
steering flow and sea breeze convergence will promote afternoon
shower and t-storm activity, mainly over interior to W-NW PR, N PR
as well as downwind of El Yunque and the local islands. A weak mid
to upper level trough is also present area today, further promoting
shower and thunderstorm development. Storm motion is also expected
to be relatively low, further prompting a limited to elevated
flooding risk.

On Friday, moisture from the wave will continue to filter into the
area with PWAT values around 1.90 to 2 inches through most of
Saturday. Shower activity will also be steered towards the islands
during the overnight to morning hours. Diurnal heating, sea breeze
convergence, local effects, and near to below normal 500 mb
temperatures, will continue to promote afternoon convection on
Friday, over similar areas as Thursday. More easterly flow can focus
convective activity over western PR on Saturday. 925mb temperature
forecasts continue to indicate values at 2 standard deviations above
normal each late morning to afternoon during the period. This
indicates an elevated to possibly significant heat risk once again
to end the week. Elevated to significant heat risks prompt the
issuance of Heat Advisories and Extreme Heat Warnings, respectively.
An elevated heat risk affects most individuals sensitive to heat,
especially those without effective cooling and/or adequate
hydration. A significant heat risk affects anyone without effective
cooling and/or adequate hydration.


.LONG TERM...Sunday through Thursday...

From Sunday through midweek, the overall weather pattern will
resemble typical seasonal conditions. A steady easterly wind flow
will transport patches of trade wind moisture across the islands
from time to time. This will favor brief overnight and early
morning showers across the U.S. Virgin Islands and eastern Puerto
Rico, followed by afternoon convection over the interior and
western portions of Puerto Rico due to sea breeze convergence and
diurnal heating. Localized heavy downpours, occasional lightning,
and ponding of water will be possible with the afternoon activity.

By Thursday, a surface perturbation is forecast to approach the region,
enhancing available moisture and instability. This will increase
the potential for more widespread showers and thunderstorms.

Overall, the long-term forecast highlights a seasonally typical
pattern through midweek, transitioning to slightly wetter and
unstable conditions late in the period as the perturbation
approaches.

Heat advisories remain possible from Sunday through Thursday, as model
guidance indicates 925 mb temperature and humidity values ranging
from the 75th percentile to greater than two standard deviations
above normal during the period.

&&

.AVIATION...
(06Z TAFs)

Mainly VFR conditions across the the terminals. SHRA/TSRA will near
or reach TISX/TIST to start the day, and will continue to be steered
towards the islands. Winds will be light from the southeast, before
increasing by 28/13Z to around 16 kts, with higher gusts and sea
breeze variations. Between 28/17-23Z, afternoon SHRA/TSRA will
affect mainly TJBQ, convective activity form El Yunque can also
reach TJSJ at this time. Sfc winds bcmg light and variable after
28/23Z.

&&

.MARINE...

From today through Friday, the shower and isolated thunderstorm
activity could increase due to an approaching weak tropical wave near
the U.S. Virgin Islands.

&&

.BEACH FORECAST...

Moderate rip current risk along the western, northern, and
eastern Puerto Rico, and Culebra through tonight, while Saint
Croix will become low by this afternoon.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Extreme Heat Warning from 10 AM this morning to 5 PM AST this
     afternoon for PRZ001>005-007-008-010-011.

     Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ012-013.

VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for VIZ001-002.

AM...None.
&&

$$

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