675
FXCA62 TJSJ 290930
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
530 AM AST Fri Aug 29 2025

.KEY MESSAGES...

* Above normal temperatures and heat indices will persist
  throughout the weekend for the islands.

* lingering moisture from the recent tropical wave, combined with
  the influence of a mid to upper- level trough will also help
  promote afternoon showers and t-storms.

* 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.

* A low risk of rip currents is expected today and during the
  Labor Day weekend across all beaches of PR and the USVI.

&&

.SHORT TERM...Today through Sunday...

Calm conditions prevailed overnight across Puerto Rico and the US
Virgin Islands. However, a few showers with brief lightning
developed over eastern Puerto Rico, resulting in rainfall
accumulations of between 0.20 and 0.70 inches. The rest of Puerto
Rico and the US Virgin Islands remained dry. Minimum temperatures
ranged from the upper 70s to the low 80s in urban/coastal areas, and
from the upper 60s to the low 70s in mountainous/rural areas. Light
and variable winds prevailed through the night.

For today, heat concerns remain relatively high as model guidance
continues to show 925 mb temperatures running above normal. As a
result, Heat Advisories are in effect for Vieques, Culebra, and the
US Virgin Islands, while Extreme Heat Warnings have been issued for
urban and coastal areas of Puerto Rico from 10 AM to 5 PM. An
elevated heat risk (Heat Advisory) poses a concern for sensitive
individuals, particularly those lacking proper hydration or cooling.
A significant heat risk (Extreme Heat Warning) means that nearly
everyone, without adequate cooling and hydration, is vulnerable to
heat-related illness. Therefore, we urge visitors and citizens to
follow the Department of Health`s recommendations to avoid being
significantly affected by the heat.

In addition to the heat, lingering moisture from the recent tropical
wave, combined with the influence of a mid to upper-level trough,
will keep precipitable water values elevated between 1.80 and 2.00
inches. Model guidance also indicates 500 mb temperatures between -6
and -8 C, supporting instability and deep convective development.
As a result, showers and thunderstorms are expected to form during
the afternoon, mainly across northwestern Puerto Rico and possibly
the San Juan metro area. While these showers may provide brief
relief after 12 PM over the northwestern sections, conditions will
otherwise remain hot and humid.

Looking ahead to the weekend, winds are expected to shift more
easterly, with models suggesting a slight reduction in moisture,
which will lower precipitable water values to around 1.501.80
inches. Still, typical seasonal weather will prevail: passing
showers during the early morning hours, followed by afternoon
convection focused mainly across western Puerto Rico. Heat concerns
will persist, as models continue to show 925 mb temperatures ranging
from above normal to above two standard deviations. Combined with
periods of strong sunshine, this will sustain an elevated risk of
heat-related impacts. Conditions will be monitored closely, and
updates will be issued as necessary to keep residents and visitors
well-informed.

.LONG TERM...Monday through Friday...

A seasonal diurnal pattern is forecast during the workweek to
start September, as patches of moisture are steered towards the
islands under east to east-southeast steering flow. Weak mid to
level troughiness can reach the area during the second half of the
workweek. Precipitable water values will be at normal values for
this time of the year, with afternoon convective activity reaching
values above 2 inches. Overnight passing showers will also
affect the eastern region. With 925 mb temperatures remaining
above normal, elevated to possibly significant, at times, heat
risk will remain during the workweek. 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. This
diurnal heating, along with orographic effects, east to east-
southeast steering flow and sea breeze convergence will promote
afternoon shower and t-storm activity, mainly over interior to
W-NW PR, as well as downwind of El Yunque and the local islands.
Localized heavy downpours, lightning, and flooding risks will be
possible with the afternoon activity. Per the 2 AM AST Tropical
Weather Outlook issued by the National Hurricane Center, a
tropical wave is forecast to emerge off the west coast of Africa
this Sunday and has a low (20%) formation chance through 7 days.

&&

.AVIATION...
(06Z TAFs)

VFR conditions across all TAF sites. Between 29/17-23Z, afternoon
SHRA/TSRA could prompt brief MVFR cond over TJBQ. Convective
activity from El Yunque can also reach TJSJ. SE winds will dominate
all sites, increasing in speed from 29/13Z to around 12 to 17 kts.
However, we anticipate occasional higher gusts, particularly during
the heaviest rainfall and due to variations in sea breezes. Sfc
winds will bcmg light after 23Z.

&&

.MARINE...

The trailing moisture from a past tropical wave, will promote
showers and posible isolated thunderstorms early today across the
local waters. Convective activity is forecast downwind of the islands
during the afternoon hours. Another weak tropical wave will enter
the Lesser Antilles by tomorrow, Saturday. Mariners can expect
moderate east to east- southeast winds and moderate chops across the
regional waters during the rest of this week and into early next
week.

&&

.BEACH FORECAST...

The risk of rip currents will remain low through the weekend, and
possibly extending through the next midweek. Even if the risk of
rip currents is low, life-threatening rip currents often occur in
the vicinity of groins, jetties, reefs, and piers.

&&

.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...MMC
LONG TERM....MRR