417
FXCA62 TJSJ 052027
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
427 PM AST Wed Jun 5 2024

.SYNOPSIS...

Troughiness at different levels across the northeastern Caribbean
will continue to enhance shower and thunderstorms development
across the regional waters and portions of the islands through
early Thursday. A Saharan Air Layer will bring drier air and
Saharan dust across the local area from tomorrow onwards. Hazy
conditions are expected mainly on Thursday and Friday. Hot
temperatures are expected through the weekend.


&&

.SHORT TERM...Today through Friday...

Thunderstorms developed this afternoon over the interior and
northwest sections of Puerto Rico, and between eastern PR and the
U.S. Virgin Islands. Rainfall amounts were generally between 2
and 3 inches with the heaviest showers. High temperatures were
between 88 and 94 degrees across the lower elevations of the
islands with heat indices ranging between 108-116 degrees before
the onset of afternoon convection. Winds were from the southeast
at 10 to 15 mph with gusts between 22-24 mph across coastal areas.

A mid-to upper-level trough pattern to our north/northwest will
continue to aid in the development of showers and thunderstorms
across the local area through at least early Thursday. At lower-
levels, a moist southerly wind flow prevails and showers could
still move at times over land areas through Thursday morning.
Although a drier air mass with Saharan dust is expected to
gradually filter from the east on Thursday, afternoon convection
is expected to develop once again across portions of the interior
and the northwest quadrant of Puerto Rico. Hazy skies are also
expected in general across the local area through Friday, with the
peak of the event on Thursday. Having said that, a gradual
decrease in shower activity is expected between late Thursday and
Friday.

The available low-level moisture content and the southeasterly
winds will promote hot conditions across the islands during the
next several days, particularly across St. Croix and most coastal
municipalities of western and northern Puerto Rico.


.LONG TERM...Saturday through Wednesday.../From Prev Forecast

The latest model guidance continues to suggest a dryer and more stable
weather pattern across Puerto Rico and the U.S. Virgin Islands as
a deeply layered ridge prevails just east of the Leeward Islands
through the weekend. The NASA Dust Aerosol Optical Thickness model
indicates the presence of Saharan Dust particles over the area.
Currently, the concentrations do not surpass 0.20. Therefore, it
is not considered as a slight to moderate dust event, and we did
not add it to our forecast grids. Nevertheless, people will
experience hazy skies, and sensible people with respiratory
illnesses could still be affected. The latest Precipitable Water
(PW) models suggest values decreasing to normal, even below normal
climatological levels for this time of the year. Most recent
guidance also shows dry air at the mid-levels of the atmosphere
and the 500 mb temperatures around -5 degrees Celsius, meaning
that if any rainfall activity does develop, it will not grow much
vertically. Therefore, we do not anticipate unstable conditions
through the weekend. However, we cannot rule out the typical
afternoon convection across the islands.

By Tuesday into midweek, we foresee a slight increase in moisture as
the Saharan Dust moves out of the area and patches of moisture
associated with another tropical wave reach the island.

Overall, during the long term, we forecast mostly stable weather
conditions across the islands, with southeasterly to east-
southeasterly winds. With this weather pattern, we anticipate warm
temperatures, and we cannot rule out the possibility that heat
products like advisories and warnings will be issued along the
lower elevations and urban areas. We encourage citizens and
visitors/tourists to stay updated with our latest weather
forecasts.


&&

.AVIATION...

(18z TAFs)

SHRA and Isold TSRA will develop ovr the central interior and
northern sections of PR steered by the prevailing southeasterly
winds. Prds of MVFR conds with the aftn convection with also brief
MVFR due to psbl SHRA/Isold TSRA at TJSJ/TJBQ til 04/23Z. Wdly SCT
SHRA and Isold TSRA will continue ovr regional waters and en route
btw islands durg prd. SCT ocnl BKN lyrs nr FL025...FL050...FL080.
SFC wnds mainly fm SE 8-12 kts with some sea breeze variations bcmg
less then 10 kts aft 05/23Z.


&&

.MARINE...

A surface high pressure north of the area will slowly move
eastwards and build into the central Atlantic by the weekend. A
surface trough will remain mainly north and west of the area. In
response, light to moderate winds will continue to prevail from
the southeast across the local waters. Isolated thunderstorms over
the offshore waters and passages are possible through Thursday
morning. The next tropical wave with better potential for squally
weather is expected by early next week.


&&

.BEACH FORECAST...

A low to moderate risk of rip currents will prevail through the
weekend, with the moderate risk mainly across the south and east
facing beaches of the islands.


&&

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

$$

SHORT TERM/BEACH & MARINE...DSR
AVIATION...RAM