807
FXCA62 TJSJ 192134
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
534 PM AST Wed Jun 19 2024

.SYNOPSIS...

For the latter half of the workweek, winds are forecast to back
and become more easterly and increase in speed. Columnar moisture
will remain at normal to above normal. Afternoon shower and
thunderstorm activity should concentrate more on interior to
western PR and downwind of the local islands. More seasonal
conditions are expected this weekend, but still with enough
moisture to generate showers and isolated thunderstorms. Hot
conditions will persist each afternoon, with little relief for
areas with the lowest cloud coverage.

&&

.SHORT TERM...Tonight through Friday...

Afternoon shower and thunderstorm activity was observed across
most of the area with the strongest activity over western and
northern municipalities. These showers and thunderstorms were fast
moving, finally moving offshore and or dissipating. The highest
rainfall amounts were reported around Manati, Barceloneta and
Arecibo, peaking at around 4.18 inches in Barceloneta. High heat
indices above 106 degrees were reported in several coastal areas,
before generalized afternoon convection and cloudiness was able
to provide relief in that aspect to most areas. Precipitable water
(PWAT) values are above normal (above 2.0 inches) over the
region. Current model guidance has the bulk of PWAT leaving the
area during the overnight hours. For Thursday and Friday, columnar
moisture will remain normal to above normal as as patches of
moisture move across the region. The interaction between a broad
surface high over the Central Atlantic and an induced surface
trough northwest of the local islands has promoted southeasterly
winds today. For tonight, remnant afternoon showers will continue
lingering and gradually dissipating while showers and possible
thunderstorms move towards the eastern and southern coastal areas
from the waters. As we head into the second half of the weekend
the surface trough will move westward and the surface high will
build, due to this winds are forecast to back and become more
easterly while increasing to moderate and locally fresh speeds.
Under these easterly winds and patches of moisture, afternoon
shower and thunderstorm activity should concentrate more on
interior to western PR and downwind of the local islands. Lows
tonight up to upper 70s and around 80 across lower elevation
areas. 925 mb temperatures should remain at normal to above normal
values.

.LONG TERM...Saturday through Wednesday...
./FROM PREV DISCUSSION...Issued at 349 AM AST Wed Jun 19 2024/

A surface high pressure centered over the eastern Atlantic will
drive the trade winds from the east during the weekend, bringing
occasional showers across eastern Puerto Rico and the Virgin
Islands, and followed by afternoon convection across western Puerto
Rico.

Early next week, a mid level ridge will build north of the
region, and the surface high pressure will strengthen as it moves
westward. At this time, an induced surface trough will approach the
area, and a tropical wave will cross the eastern Caribbean. The
moisture from these surface features will bring an increase in
showers to the area, mainly for the Virgin Islands, local waters and
eastern Puerto Rico. Accumulations are not expected to be too
significant because the low level steering flow will be enhanced.
Saharan dust will follow on Tuesday, lasting through Wednesday. Then
on Wednesday, another trough will dig from the northeast, shifting
the winds from this direction. All these days, afternoon convection
is anticipated, mainly for the interior and western Puerto Rico. The
activity could be strong, with possible lightning, and urban and
small stream flooding developing.

The heat risk will be elevated all these days, impacting outdoor
activities, and those without effective cooling or poorly hydrated.

&&

.AVIATION...

(18Z TAFS)

Tempo MVFR conds are possible at TJBQ/TJSJ thru 19/23z, and mostly
VCSH elsewhere during the overnight hours. Otherwise, VFR conds
expected to prevail thru 20/15z. TSRA developing once again aft
20/16z across central and western PR, causing VCTS at TJBQ/TJPS. ESE
winds up to 15 kt will prevail in general across all terminals, with
land breeze variations during the night. HZ due to Saharan dust but
VSBY should remain P6SM.

&&

.MARINE...

Surface high pressure over the Atlantic will promote moderate to
locally fresh easterly winds through the rest of the week. Passing
showers and isolated thunderstorms accompanying and trailing a
tropical wave will continue to affect the coastal waters and local
passages resulting in localized hazardous marine conditions.

&&

.BEACH FORECAST...

For tonight, there is a moderate risk of rip currents for St.
Croix and eastern Vieques. For tomorrow, the moderate risk of rip
currents will spread to Culebra as well as to the northern,
southwestern and southeastern coastline of Puerto Rico. For
tomorrow night, the moderate risk of rip currents will spread to
the northern USVI.

&&

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

$$

SHORT TERM....CAM
LONG TERM.....MRR
PUBLIC DESK...YZR