511
FXCA62 TJSJ 071857
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
257 PM AST Sat Jun 7 2025

.KEY MESSAGES...


* Increasing surface winds will likely generate moderate to
  locally fresh winds, resulting in wind-driven seas. Therefore,
  small craft operators should exercise caution. Small Craft
  Advisories may be issued across the offshore waters by midweek.

* Warmer-than-normal temperatures are likely to continue through
  the weekend across most coastal and lower elevations of the
  islands, with the possibility of a Heat Advisory on Monday.

* Above-normal moisture associated with a tropical wave, along
  with increasing instability, might result in a rise in showers
  and thunderstorms this week.

&&


.SHORT TERM...Tonight through Monday...

The morning was relatively quiet, with a few passing showers over
the waters occasionally moving inland across the windward sections
of the islands. Rainfall accumulations from this activity were
minimal. By noon, gusty wind conditions had already been reported,
with several coastal weather stations recording sustained winds in
the mid to upper 20s mph range. Ponce Mercedita Airport even
reported wind gusts reaching 30 mph. A surface high-pressure over
the central Atlantic is expected to continue strengthening in the
short term, maintaining breezy to locally windy east-southeast
conditions across the islands coastal areas.

The frequency of showers and the areal coverage of afternoon
convection are expected to gradually increase through the short-term
forecast period. At upper levels, an omega pattern has developed,
featuring a low-pressure over Cuba and the central Atlantic, with
weak ridging in place over the local area. This pattern is expected
to dissipate as the eastern low pressure strengthens and the western
low near Cuba shifts slightly eastward into the northeastern
Caribbean. This evolution will promote marginal instability aloft,
supporting the development of deep convection. In terms of
moisture, the 07/12Z TJSJ sounding and current GOES-19
Precipitable Water satellite data indicate well below-normal
values ranging from 1.2 to 1.3 inches across the region. However,
a surface perturbation just east of the CWA, with PWAT values
between 1.6 and 1.9 inches, is forecast to gradually move over the
area from this evening through tomorrow.

Additionally, a tropical wave, currently located near 47W, is
expected to approach the region by late Monday. This tropical wave
will likely help sustain above-normal moisture levels across the
forecast area. The combination of increased moisture and marginal
upper-level instability will lead to a rise in shower activity,
particularly during the nighttime and morning hours across windward
coastal areas, and in the afternoon due to diurnal heating and sea
breeze convergence interacting with the aforementioned conditions.
As a result, expect a limited to elevated flooding threat each day,
with a higher potential during the afternoon hours, especially
across western Puerto Rico.

Warmer-than-normal temperatures, driven by an east-southeast wind
flow and high humidity, will result in elevated heat index values,
particularly across urban and coastal areas. During certain periods,
conditions may even reach Heat Advisory criteria. This level of heat
can affect most individuals sensitive to high temperatures,
especially those without access to adequate cooling or hydration.

&&

.LONG TERM...
/PREV DISCUSSION... /issued 404 AM AST Sat Jun 7 2025/

Current model guidance has precipitable water (PWAT) values at up to
above normal to start the long term period as moisture, in part from
a tropical wave over the Caribbean Sea, is steered into the local
islands under east-southeast flow. However, a Saharan Air Layer
(SAL) will also reach the islands, promoting hazy skies. While PWAT
values will gradually decrease, a more notable mass of drier air is
forecast to arrive by Friday. A surface high pressure over the
Atlantic will continue building during the period, promoting breezy
to locally windy easterly to east-southeasterly steering flow. A mid-
level ridge will be present to start the period, but it will
gradually weaken as a mid-level low moves into the central Atlantic.
The typical diurnal pattern will continue with patches of moisture
and showers reaching windward sectors of the islands, especially
during the mornings and overnight hours, and with afternoon showers
and thunderstorms mainly over interior to western Puerto Rico due to
sea breeze convergence, diurnal heating and local effects. Lines of
showers can also develop downwind of the local islands and El
Yunque. An elevated flood potential will persist over interior to
western Puerto Rico. Highs will be in the upper 80s to low 90s at
lower elevations and coastal areas , with heat indices over 100
degrees. A limited heat risk will persist for most coastal and lower
elevation areas. Lows will be in the 60s for higher elevations of
Puerto Rico and in the 70s to around 80 over lower elevations of the
islands. Although moisture will gradually decrease, the frequency of
showers could be higher due to an upper level trough from the
northeast, and another tropical wave moving into the Caribbean Sea
by the end of the forecast period.

&&

.AVIATION...

(18Z TAFs)

Mostly VFR conds for all TAF sites. Dvlmpt of TSRA over western PR
might bring VCTS over TJBQ, with a chance of movg inside TAF site,
and AMD remains possible. PROB30s for TIST and TISX due to -SHRA
movg around 08/02z, then for TJSJ around 08/04z, and for TJPS
near 08/14z, reducing CIGs/VIS and promoting temporary MVFR
conds. E-ESE winds btwn 11-16 kt with gsts up to 25 kt btwn 07/18
through 07/23z, reducing btwn 5-9 kt.

&&

.MARINE...

A surface high pressure across the central Atlantic will continue to
promote moderate to locally fresh trade winds, gradually shifting
east to southeast today. Isolated thunderstorms are expected to
develop each afternoon over the western waters of Puerto Rico,
small craft should exercise caution. A tropical wave will move
across the eastern Caribbean around Tuesday.

&&

.BEACH FORECAST...

Increasing winds will very likely promote a moderate risk of rip
currents for the northern and eastern beaches of Puerto Rico later
tonight. The risk should spread tomorrow across the beaches of
Culebra and the U.S. Virgin Islands, persisting for the next few
days. Beachgoers should exercise caution, as life-threatning rip
currents are possible over these areas.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM...CVB
AVIATION...MNG
LONG TERM...MRR