153
FXCA62 TJSJ 042121
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
521 PM AST Tue Jun 4 2024

.SYNOPSIS...

A wet pattern will continue through at least Thursday, as
southerly winds continue to steer warm and moist air over the
area, an approaching tropical wave will also help in maintaining
favorable conditions for active weather. Therefore, the risk of
flooding rains will range from limited to elevated across most of
the forecast area. Improving conditions are forecast by the end
of the workweek into the weekend.

&&

.SHORT TERM...Tonight through Thursday...

During the morning hours, showers and t-storms continued to affect
the eastern region and islands, steered from the Caribbean Sea by
southeasterly winds. This activity affected sectors of the southern
half of PR, eastern PR and the local islands. Strong activity
focused over St. John during the early morning hours and over St.
Croix by late morning to early afternoon. Several official and
unofficial stations reported highs ranging in the upper 80s to mid
90s, with the highest values seen across the northern coastline
Puerto Rico. The LMM Airport station reported a high of 94 degrees
Fahrenheit, tying the record with 2023 and 2022. These hot and humid
conditions resulted in heat indices climbing up to around to above
110 degrees across several coastal areas. Although heat indices
are subsiding, , some localized coastal and urban areas will
experience heat index values above 100F degrees until sunset.

Southerly winds will continue through the period a subtropical high
is located across the central to northeast Atlantic and a broad and
elongated trough extends northwards north of the region from the
central and eastern Caribbean. Without sea breeze and sea breeze
convergence, afternoon activity has been limited across Puerto Rico,
with high heat indices continuing across the islands. Deep layered
tropical moisture will continue to be steered into the region under
southerly flow promoting precipitable water (PWAT) values to be
above normal (2.0 inches) for this time of the year across the
region staying at around 2.2 inches and increasing on Wednesday to
around 2.4 inches. An approaching tropical wave will also help in
maintaining favorable conditions for active weather. It`s not until
late Thursday that model guidance has PWAT values below 2 inches
starting to filter into the islands (along with a Saharan Air
Layer). Wednesday continues to be the wettest day with more
favorable conditions to observe flooding. Model guidance continues to
suggest 925 mb temperatures remaining up to 2 standard deviations
above normal.

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

./FROM PREV DISCUSSION...Issued at 513 AM AST Tue Jun 4 2024/

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...

(18Z TAFS)

Aftn SHRA and Isold TSRA will cont to develop across
the central interior and northern sections of PR steered by the
persistent southerly wind flow. This will result in prds of MVFR
conds with the aftn convection and brief MVFR psbl at most TAF
sites til 04/23Z. Wdly SCT SHRA with Isold TSRA psbl mainly over
the Caribbean waters and local passages en route btw islands durg
prd. SFC wnds fm SE-S 12-15 kts bcmg 10 kts or less fm S aft
04/23Z.

&&

.MARINE...

The strong sub-tropical high pressure across the central and
northeast Atlantic along with a broad and elongated trough
extending northwards across the region from the central and
eastern Caribbean will promote a moderate to locally fresh south
to southeasterly wind flow. The moist southerly flow will maintain
the potential for showers and isolated thunderstorms across the
regional waters especially during the overnight and afternoon
hours. This will also aid in increasing winds and seas, especially
across the Caribbean Waters and local passages each day. As a
result small craft should exercise caution.

&&

.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....CVB
LONG TERM.....MRR
PUBLIC DESK...RVT