998
FXCA62 TJSJ 040913
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
513 AM AST Tue Jun 4 2024

.SYNOPSIS...

The wetter pattern is still forecast through at least mid-week as
a tropical wave continues to affect the region maintaining high
moisture content across the area. Therefore, the risk of flooding
rains will range from limited to elevated across most of the
forecast area. Improving conditions are foreseen by the end of the
workweek into the weekend.

&&

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

The weather conditions prevailed variably cloudy, and the east-
southeast winds pushed additional moisture across PR and the USVI.
The minimum temperatures ranged from the upper 70s to low 80s along
the coast to the upper 60s and low 70s across mountains and valleys.
The Doppler radar detected showers and thunderstorms moving from the
Caribbean Sea across the USVI and PR`s windward sections, making
their way further inland. Gusty winds and ponding of water in roads
and poorly drained areas were likely due to the thunderstorms.
Hazardous marine conditions due to a cluster of strong thunderstorms
affected the USVI`s eastern surrounding waters. Thus, a Special
Marine Warning was issued.

A surface trough north of the islands induces a southeasterly wind
flow, pooling plenty of tropical moisture from the Caribbean Sea,
creating an unstable weather pattern. This could lead to potentially
hazardous conditions, with flooding of urban areas, roads, and small
streams likely, and flash and river floods possible. Additionally,
the available moisture combined with the expected maximum air
temperature will produce muggy heat index values in the upper 90s
and surpass 100 degrees Fahrenheit again today, especially when rain
activity is absent or after brief showers.

The model guidance consistently suggested values near or above 2.25
inches, above the normal values for the San Juan area`s local
climatology for June, extending into the middle of the week.
Wednesday will be the wettest day with the more favorable conditions
to observe flooding.

Our latest guidance, based on the GFS model, indicates a slower
drying out of the region than the previous runs, with plenty of
moisture expected through the late Thursday night hours or early
Friday morning. This aligns with the NASA Dust Extinction (Aerosol
Optical Thickness) guidance, which suggests the arrival of more
pronounced African Desert Particles filtering across the region.

&&

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

By the end of the work week, we will gradually reach the
anticipated drying and stable weather pattern across Puerto Rico
and the U.S. Virgin Islands as a deeply layered ridge builds and
holds just east of the Leeward Islands. The NASA Dust Aerosol
Optical Thickness model indicates the presence of Saharan Dust
particles over the area from Friday into the weekend. Currently,
the concentrations do not surpass 0.20 on those days. Therefore,
it was not added to our forecast grids, particularly because it
is not be considered a slight to moderatedust event.Nevertheless,
people will experience hazy skies, and the ones with respiratory
illnesses could still be affected.

The latest climatological Precipitable Water(PW) models continue to
suggest values above the 75th percentile and dry air at the mid-
levels with 500 mb temperatures around -4 to -5 degrees Celsius.
This means that there will be sufficient surface moisture across
the region, but conditions at the mid-levels of the atmosphere
will not be favorable to the vertical development of any shower
activity that does develop. At this time, we anticipate showers
forming along the northwestern quadrant of Puerto Rico,
particularly during the afternoon hours.

On Monday and Tuesday, 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 over South
America/southeastern Caribbean waters are brought into the
region.

During the long-term period, southeasterly winds will prevail across
the islands, meaning that warm temperatures will prevail mostly
across the islands. With the warm temperatures and the available
moisture, we anticipate the issue of heat advisories in low and
urban areas.

&&

.AVIATION...

(06z TAFs)

The unstable weather pattern will continue today and tomorrow with
the arrival of SHRA/TSRA across the local flying area. Therefore, we
can expect brief periods of MVFR or brief IFR conditions at local
terminals (mainly through 04/12z and later in the afternoon 04/16-
22z). Winds will prevail from the SE/ESE at 5 to 10 kt, then between
10-15 kt after 04/13z, with higher gusts (especially near TSRA) and
sea breeze variations.

&&

.MARINE...

A stationary front and a sub tropical high pressure across the
Western Atlantic will promote a moderate to locally fresh south to
southeasterly wind flow. A wetter pattern is anticipated through at
least mid-week as a tropical wave continues to affect the region
maintaining high moisture content across the area with increasing
seas and winds, as a result small craft should exercise caution,
especially across the Caribbean Waters and local passages.

&&

.BEACH FORECAST...

There is a moderate risk for most beaches from western, southern,
and southeastern Puerto Rico, Vieques, Culebra, and USVI. The northern
beaches of Puerto Rico have a low risk of rip currents. The risk
of rip currents is expected to remain between low and moderate
through at least midweek, then return to low by the end of the
workweek into the weekend.

&&

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

$$

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