991
FXCA62 TJSJ 102006
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
406 PM AST Mon Jun 10 2024

.SYNOPSIS...

Warm conditions will persist through tomorrow, and it`s crucial
to note that an Excessive Heat Watch will be in effect across all
coastal areas of Puerto Rico and the US Virgin Islands. This watch
is a significant indicator of potentially dangerous heat levels,
urging residents, tourists, and businesses to stay informed and
take necessary precautions. By Wednesday, a tropical wave will
move over the Caribbean Waters, increasing moisture content and
the potential for showers and warmer conditions. Tranquil marine
conditions should prevail for the next five days, with seas up to
4 feet and a low risk of rip currents.

&&

.SHORT TERM...Tonight through Wednesday

As yesterday, another melting day was observed across the tropical
islands. The mid-level rise continued to provide stable weather
conditions across the islands under the warmer trend, with minimal
rainfall activity across the northwestern side of Puerto Rico.
According to some unofficial stations across the islands, heat
index values reached 111F in the northwestern quadrant and
between 105F and 110F in the north-central areas of Puerto Rico.
According to the official climate site at the Luis Munoz Marin
Airport in Carolina, the maximum temperature reached 91F.

The short-term forecast remains on track. Stable weather
conditions will prevail, resulting in the mid-level ridge that
continues to hold across the region. Meanwhile, at the surface, a
broad area of high pressure extending from the eastern to the
central Atlantic will result in east-southeasterly winds over the
CWA. Under this wind pattern, the islands will continue to
experience a warmer trend, with heat indices between 100F and
112F across all coastal areas and urban sections. Given the
expected conditions for tomorrow, an excessive heat watch is in
effect for all coastal areas for all the islands. Remember, the
heat watch/advisory and warning might not be in effect for some
interior municipalities; however, heat indices resulting in heat
exhaustion are possible, especially over San Sebastian, Lares,
Sabana Grande, and areas near Caguas.

Similar surface conditions will hold from Tuesday to Wednesday with
the east-southeasterly wind, the broad ridge, and some tropical
moisture from a distant tropical wave passing over the Caribbean
Waters. However, at the upper levels, a weak upper-level trough
will sink southwestward, bringing the northwestern side of the
forecast area. Conditions will become slightly favorable for upper
cloudiness and some increase in showers over the western
sections. Having said that, no widespread shower activity is
expected, so the forecast calls for localized showers in the
afternoon over the western interior.

.LONG TERM...Thursday through Monday...from previous discussion at
436 AM AST Mon Jun 10 2024...

Current model guidance suggests normal to below normal Precipitable
Water (PWAT) values as a tropical wave will be southwest of the
area to start the period. However, an area of normal to above
normal PWAT will start to approach the islands from the northeast
increasing PWAT values through Friday. This is due to the remnants
of a past frontal boundary being pushed towards the area by a
high pressure system over the Atlantic. High pressure aloft will
also strengthen over the Western Caribbean through the period.
Winds through Friday are forecast to be more east to east
northeasterly, which could bring some slight relief in terms of
warm temperatures although model guidance continues to suggest
above normal 925 mb temperatures. Winds are forecast, however, to
become more southeasterly by the weekend and through the rest of
the period. This will help promote warm temperatures once again.
PWAT values return to normal for the weekend with another plume of
moisture with above normal to normal values possibly reaching the
area by next week. Most available moisture will remain below 850
mb, with only a slight increase in moisture through the mid-levels
for the weekend. Saharan dust particles will linger to start the
forecast period.


&&

.AVIATION...
VFR conditions are expected at all TAF sites during the next 24
hours. At least through 10/22Z, afternoon VCSH/SHRA may briefly
impact operations across TJBQ. E-ESE winds at 10-15 knots, becoming
at 10 knots or less overnight.

&&


.MARINE...
A mid to upper level ridge is promoting generally stable conditions
across the local waters. Surface high pressure extending from the
northeastern to central Atlantic and north of the area will continue
to promote up to moderate to fresh east-southeasterly winds through
midweek. A tropical wave is expected to increase the potential for
showers and isolated thunderstorms mainly across the Caribbean waters
and local passages on Wednesday.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Excessive Heat Warning until 6 PM AST this evening for
     PRZ001>003-005-007-008-010-011.

     Excessive Heat Watch from Tuesday morning through Tuesday
     afternoon for PRZ001>003-005-007-008-010>013.

     Heat Advisory until 6 PM AST this evening for PRZ012-013.

VI...Excessive Heat Watch from Tuesday morning through Tuesday
     afternoon for VIZ001-002.

     Heat Advisory until 6 PM AST this evening for VIZ001-002.

AM...None.

&&

$$

SHORT TERM...LIS
AVIATION...OMS
PUBLIC...MMC