342
FXCA62 TJSJ 080900
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Tue Jul 8 2025

.KEY MESSAGES...

* Moderate to high concentrations of Saharan dust are expected to
  return during the second part of the workweek, resulting in hazy
  skies, reduced visibility, and poor air quality.

* Breezy conditions expected on Tuesday and Wednesday. Choppy seas
  and a moderate risk of rip currents will persist over the next
  few days. These may create hazardous conditions.

* Diurnally induced afternoon showers and isolated thunderstorms
  are expected over portions of the Cordillera Central and western
  PR each day. Passing showers will continue across the USVI and
  eastern sections of PR during the night/early morning hours.

&&

.SHORT TERM...Today through Thursday...

Partly cloudy skies prevailed during the overnight hours across the
islands. Passing showers were noted in and around eastern, northern,
southeastern Puerto Rico, and across St. Croix. The Doppler radar
estimated between half to three quarters of an inch of rain with the
most persistent showers in northeastern and southeastern PR. Minimum
temperatures were from the mid-60s to low-70s across the higher
elevations of Puerto Rico to the upper 70s and low 80s across the
lower elevations of the islands. The wind was light from the east,
however, gusts between 20 and 25 mph were observed with the showers.

An upper-level low over the central Caribbean Sea and an upper-level
ridge stretching over the area from the Tropical Atlantic will
continue to briefly promote divergence aloft today. This is likely
enhancing the intensity of the overnight/early morning showers, and
could cause some showers to grow into short-lived thunderstorms
across the local waters. Meanwhile, a tropical wave far south of the
region will continue to move west and away of the area by this
evening. At the lower levels, a broad ridge building from the
central Atlantic will promote east to southeast winds for the next
few days. The higher moisture content near the surface and these
winds will promote normal to above normal temperatures each day and
a limited heat risk will persist for the lower elevations and urban
areas of the islands.

A wind surge will bring scattered showers and stronger winds across
the area from tonight through Thursday. Another tropical wave with a
band of moisture of near 2.00 inches of Precipitable water content
will stream across the area on Thursday. However, higher
concentrations of Saharan dust mixed with the tropical wave could
hinder widespread convection development. Having said that, the
overall available moisture content is forecast to remain around
normal levels, fluctuating in general between 1.50-1.80 inches
through at least Thursday afternoon. Therefore, we expect a similar
weather pattern each day with passing showers across the
USVI/Eastern half of PR during the night/early morning hours,
followed by diurnally induced afternoon showers and iso
thunderstorms over portions of central and western PR, and streamers
developing downwind of the USVI and from el Yunque area. Most of
this activity across PR will cause ponding of water on roads and
poor drainage areas, and urban and small stream flooding where
thunderstorms develop.

.LONG TERM...Friday through Tuesday...

The inherited forecast remains on track. The latest model guidance
continues to support a surface wind surge crossing the region on
Friday, leading to a brief increase in low-level moisture. This may
support isolated to scattered showers early in the day. However, a
significantly drier air mass is expected to filter in by late Friday
and continue through the upcoming workweek, suppressing widespread
convection. At the same time, mid- to upper-level dry air and a
reinforcing trade wind inversion will further limit vertical cloud
development. Additionally, the arrival of a Saharan Air Layer
will contribute to hazy skies, reduced visibility, and potential
impacts on air quality, especially for sensitive groups. This
dusty and dry environment will also act to suppress rainfall
through Saturday. Breezy to windy conditions will prevail both
Friday and Saturday, with easterly winds supporting above-normal
temperatures, particularly in coastal and urban areas.

By Sunday, the Tropical Upper-Tropospheric Trough (TUTT) is forecast
to shift westward toward Hispaniola. This transition, combined with
the approach of easterly trade wind disturbances, will begin to
increase atmospheric moisture over the region. As a result, rain
chances will rise on Sunday afternoon, with a more favorable
environment for convection.

Monday and Tuesday will likely feature the highest rainfall
potential as deeper tropical moisture becomes established across
Puerto Rico and the U.S. Virgin Islands. Scattered showers and
thunderstorms are expected each afternoon, especially in western and
interior sections.
Although the threat of excessive rainfall remains low until late
Sunday into Monday, other weather concerns.

&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions are expected to prevail across all terminals.
However, SHRA en route from the Leeward terminals may cause brief
periods of MVFR cigs and -RA. Then, diurnally induced afternoon TSRA
over northwestern PR should lead to tempo MVFR conds at TJBQ fm
07/17-21z. Elsewhere, mostly VCSH and brief -RA periods expected. HZ
will gradually increase during the next day or so, but VSBY should
remain P6SM. However, higher concentrations of Saharan dust return
from Thursday onward and visibilities could drop to 5-6 SM. Winds
will continue E-ESE at 14-19 kt with sea breeze variations and
higher gusts aft 08/14z.

&&

.MARINE...

Moderate to locally fresh winds will create choppy seas across local
waters over the next several days, small craft should exercise
caution. Small Craft Advisories will possibly be issued later on for
Wednesday. Afternoon thunderstorms may impact coastal waters and
local passages, particularly over western Puerto Rico and the Mona
Passage each day. Showers and thunderstorm chances increase on
through Thursday with the passage of tropical waves. Saharan dust is
expected to return later in the workweek.

&&

.BEACH FORECAST...

Increasing winds over the next several days will promote a
moderate risk of rip currents across the eastern, northern, and
southeastern beaches of Puerto Rico, Vieques, Culebra, St. Thomas. and
St. Croix. Life- threatening rip currents often occur in the
vicinity of groins, jetties, reefs, and piers.

&&

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

$$

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