523
FXCA62 TJSJ 112119
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
519 PM AST Tue Jun 11 2024

...EXCESSIVE HEAT WATCH IN EFFECT FROM WEDNESDAY MORNING THROUGH
WEDNESDAY AFTERNOON...

.SYNOPSIS...Excessive heat continues in the area. A tropical
wave will pass well to the south of the area with some troughing
here. Better moisture from an old frontal boundary will move in on
Wednesday night with increasing showers. Another weak trough will
move through the area on Friday followed by warmer weather with
heat warnings or advisories likely.

&&

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

High pressure at upper levels continues over the western Caribbean
and the western tropical Atlantic with some ridging north
northeast of the area as well. Mid level high pressure continues
over and north of the area to set the stage for temperatures 4 to
5 degrees above normal in San Juan and 3 to 4 degrees above normal
in Saint Croix. A tropical wave will move through the southern
Caribbean and some moisture will move in the east southeast flow
to arrive in the U.S. Virgin Islands early Wednesday evening. This
will increase shower activity for Puerto Rico late Wednesday
night and Thursday. Moisture from the remnants of an old cold
front will move in from the northeast on Wednesday night and
Thursday that will increase shower activity and cool temperatures
somewhat. Also an upper level trough will move into the area from
the west that will give a weak boost to instability in the area on
Wednesday afternoon and leave a cut-off low just north of Lake
Maracaibo, Venezuela Thursday through Friday.


.LONG TERM...Friday through Tuesday... amended from 456 AM AST
Tue Jun 11 2024

Current model guidance suggests Precipitable Water (PWAT) at normal
values to start the period with only patches of higher PWAT
values moving through the islands, remnants of a past frontal
boundary being pushed towards the region by a high pressure system
over the Atlantic, under a weak surface trough. PWAT values
remain normal, 1.6 to 2.0 in, for the weekend with another plume
of moisture related to a tropical wave, with above normal PWAT
values, possibly reaching the area by Tuesday. Most available
moisture will remain below 850 mb, with only a slight increase in
moisture through the mid-levels for Friday, Sunday and Monday. A
more notable increase in mid level moisture is forecast by
Tuesday. High pressure aloft will also strengthen over the Western
Caribbean through at least the weekend. Surface winds to start
the period are forecast to be more easterly, which could bring
some slight relief in terms of warm temperatures although model
guidance continues to suggest above normal 925 mb temperatures.
To reiterate, On Friday, another trough with a weaker pulse of
moisture will move through the area to maintain the chances of
showers in the area but will be followed by more southeasterly
winds by the weekend and through the rest of the period. This
will help promote warm temperatures once again when heat warnings
or heat advisories will likely be necessary. Saharan dust particles
will linger to start the forecast period and increase on
Saturday.

&&

.AVIATION...
(18Z)
VFR conditions will persists for all the TAF sites during the
period. Winds will become more fresh today increasing from the E-SE
at 15 knots with gusty winds and sea breeze variations. VCSH are
possible over TIST & TISX for 12/15Z as moisture reach the
islands.

&&

.MARINE...Surface high pressure extending from the northeastern to central
Atlantic and north of the area will continue to promote moderate to
fresh east to east-southeasterly winds through midweek. A tropical
wave will pass well south of the area tomorrow. For the second
half of the week, winds will be up to moderate and become east-
southeasterly to southeast by the weekend.

&&

.BEACH FORECAST...

A moderate risk of rip currents exists for southwestern,
southeastern Puerto Rico and Saint Croix tonight with a low risk
elsewhere. Tomorrow Saint Croix will continue with a moderate risk
of rip currents, but the moderate risk for Puerto Rico will move
to the northwest and north central coasts on Wednesday.

.CLIMATE...

Another warm day for Puerto Rico with a high of 93
degrees and a low so far of 82 degrees. This will tie the record
for the maximum and would break the old record of 80 degrees set
in 1981 for the minimum.

&&

.PREV DISCUSSION... /issued 1031 AM AST Tue Jun 11 2024/


SHORT TERM...Today through Thursday...

An overnight radar and satellite imagery analysis indicated partly
to variable cloudy skies over the local islands, primarily due to a
layer of mid-to-upper level clouds moving in from the southwest. A
few light showers brushed the northeast coast of Puerto Rico, and
some moved across Culebra and the northern US Virgin Islands, but
they left minimal rainfall. Reports once again highlighted warm
overnight low temperatures above 80 degrees Fahrenheit, not only in
eastern Puerto Rico and the local islands but also in inland areas
of the San Juan-Bayamon-Caguas metropolitan area and parts of
western and southern Puerto Rico. Coastal observation sites and
local buoys have also recorded warm low temperatures, hovering
around 85 degrees Fahrenheit. This scenario offers little overnight
relief and will ultimately exacerbate the region`s ongoing heatwave
situation. Winds were mainly light to calm and variable.

Weather conditions throughout the forecast period should change very
little from the persisting stable and warm pattern that has
dominated the region in recent days, mainly due to consistent mid-
level ridging and prolonged drier-than-normal periods. Driven by a
surface high pressure meandering well to the north of the local
islands, east-to-east-southeast trade winds, with peak daytime wind
speeds ranging from 15 to 20 mph, will gradually weaken and turn
east-northeasterly from Wednesday night onward, influenced by a weak
surface trough to the northeast.

Significant moisture variability will likely occur throughout the
forecast period, with precipitable water values fluctuating between
1.4 and 2.0 inches due to intermittent drier and wetter patches.
Despite these variations, with brief wet periods, showers are likely
to be sparse and highly localized, predominantly caused by daytime
heating over the far western and northwestern areas of Puerto Rico.
An increase in passing showers may occur by Wednesday night,
influenced by a nearby tropical wave, and again by Thursday night
due to the approaching surface trough. However, no flooding is
expected from the anticipated rainfall.

Dangerously hot conditions are likely again today, prompting
Excessive Heat Warnings from 9 AM to 6 PM AST for lower elevations
and coastal areas of northern and western Puerto Rico. These
conditions pose a serious risk to anyone without adequate cooling or
hydration. Heat Advisories are also in effect for the remaining
lower and coastal areas of Puerto Rico and Vieques, Culebra, and the
US Virgin Islands, indicating a significant risk for individuals
sensitive to heat. When outdoors, take extra precautions: wear
lightweight, loose-fitting clothing and limit strenuous activities
to early morning or evening. Staying hydrated and recognizing signs
of heat exhaustion are crucial. Since dangerous hot conditions will
likely continue, an Excessive Heat Watch is now in place for
Wednesday.

LONG TERM...Friday through Tuesday...

Current model guidance suggests Precipitable Water (PWAT) at normal
values to start the period with only patches of higher PWAT
values moving through the islands, remnants of a past frontal
boundary being pushed towards the region by a high pressure system
over the Atlantic, under a weak surface trough. PWAT values
remain normal, 1.6 to 2.0 in, for the weekend with another plume
of moisture related to a tropical wave, with above normal PWAT
values, possibly reaching the area by Tuesday. Most available
moisture will remain below 850 mb, with only a slight increase in
moisture through the mid-levels for Friday, Sunday and Monday. A
more notable increase in mid level moisture is forecast by
Tuesday. High pressure aloft will also strengthen over the Western
Caribbean through at least the weekend. Surface winds to start
the period are forecast to be more easterly, 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. Saharan dust particles will linger
to start the forecast period and increase on Saturday.

AVIATION...

(06Z TAFS)

VFR conditions will prevail across all terminals during the next 24
hours. Light to calm, variable winds will turn from the E-ESE at 14-
18 knots between 11/13-22Z, accompanied by higher gusts and sea
breeze variations. VCSH may develop between 11/16-22Z near TJBQ and
TJSJ, but chances are very low.

MARINE...

Surface high pressure extending from the northeastern to central
Atlantic and north of the area will continue to promote moderate to
fresh east to 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
by tomorrow. For the second half of the week, winds will be up to
moderate and become east-southeasterly by the weekend.

BEACH FORECAST...

Moderate risk of rip currents for St. Croix and SW Puerto Rico today
and tonight. Moderate risk forecast for southeastern PR tonight.
Low risk elsewhere.

&&

.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 Wednesday morning through Wednesday
     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 Wednesday morning through Wednesday
     afternoon for VIZ001-002.

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

AM...None.

&&

$$

SHORT TERM/MARINE...WS
UPPER AIR/PUBLIC....MMC
AVIATION/LONG TERM...CAM