283
FXCA62 TJSJ 241737
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
137 PM AST Sat May 24 2025

.KEY MESSAGES...

* Warm temperatures are expected to prevail each day, especially
  along coastal and low elevated municipalities and islands.

* Breezy with passing showers, but the strongest showers are
  expected each afternoon along the interior and western Puerto
  Rico.

* Saharan dust will approach the islands on Monday and Tuesday,
  resulting in hazy skies, reduced visibilities and a
  deterioration in air quality.

&&

.SHORT TERM...Rest of today through Monday...

Very few showers were observed this morning under a strong
easterly breeze. Temperatures are warming up, as it expected for
late May, with heat indices hovering around the 100 degree mark
for the coastal areas of Puerto Rico, and also for the Virgin
Islands. With strong diurnal heating, showers are expected to
develop along the west of Puerto Rico. Since the winds are strong,
showers should develop closer to the coast, and move quickly.
Therefore the risk of flooding is limited for this area.

A broad surface high pressure centered over the eastern Atlantic
will maintain enhanced trade winds across the region, coming out
of the east or slightly southeast at 15-18 kts. At the mid-levels,
the airmass is dry, with relative humidities below 35% above
18,000 feet. This means that the patches of moisture dragged by
the trade winds will be shallow in nature, moving quickly and
without leaving significant rainfall accumulation. For the start
of the workweek, a tropical wave approaches, but the moisture
field will stay mostly over the Caribbean Sea. Saharan dust will
move in too on Monday, with high concentrations anticipated. Skies
are expected to be hazy, with reduced visibilities and some
impacts to health are also anticipated.

Seasonably warm temperatures are expected too, with highs in the
upper 80s and low 90s in coastal and low elevated areas. Heat
indices are expected to hover around 100 degrees each afternoon.
Stay hydrated!

.LONG TERM...Tuesday through Saturday.../from prev discussion/

Hazy skies due to a lingering Saharan Air Layer with suspended
Saharan dust will continue on Tuesday. Although drier air aloft
will persist on Tuesday, sufficient low-level moisture content is
also expected, therefore, diurnally induced afternoon showers with
iso thunderstorms cannot be ruled over western PR. Then, through
at least Thursday, the area will remain under the influence of an
upper-level trough over Hispaniola and a weak mid-level ridge east
of the Leeward Islands. This will cause the 500 mb temperatures
to drop to around -8C and the precipitable content to remain near
1.75 inches, which is in the higher end of the 50th percentile for
this time of the year. Therefore, afternoon thunderstorms are
likely to develop over portions of the Cordillera and western PR.
These thunderstorms may cause strong gusty winds and locally heavy
rainfall that can lead to urban and small stream flooding. For
the end of the forecast cycle, the 500 mb temps are expected to
warm about 2 degrees, suggesting more stable conditions aloft.
However, at the lower levels, another tropical wave is forecast to
enter the eastern Caribbean and increase the precipitable water
content once again between 1.75 and 2.00 inches.


&&

.AVIATION...
(18z TAFs)

VFR conds are expected across all TAF sites. However, we forecast
the development of SHRA along western and central Puerto Rico,
creating mountain obsc thru 24/23Z. Winds will prevail from the E at
15-20 kts with higher gusts ranging from 21-28 kts and sea breeze
variations. Winds will become slightly light and variable after
24/23Z, returning from the E at around 15-20 kts tomorrow after
25/13-14Z.

&&

.MARINE...
A surface high pressure building over the North Atlantic Ocean will
promote moderate to locally fresh easterly winds through early next
week. A tropical wave will move mainly south of the region and across
the Caribbean Sea between Sunday and Monday. Isolated thunderstorms
are expected to develop across the western coastal waters of Puerto
Rico each afternoon.

&&

.BEACH FORECAST...
Increasing winds will result in beaches reaching a moderate risk
of rip currents, mainly for the eastern and northern half of
Puerto Rico, Vieques, Culebra, and for all of the Virgin Islands.
Life- threatening rip currents could occur in these places.

&&

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

$$

RADAR/AVIATION...MMC
UPPER AIR/DISCUSSION....ERG