325
FXCA62 TJSJ 110856
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
456 AM AST Tue Jun 11 2024

.SYNOPSIS...

Hot conditions continue. Excessive Heat Warnings are in effect
from 9 AM to 6 PM AST for all lower elevations and coastal areas
of Puerto Rico. Heat Advisories are in effect from 9 AM to 6 PM
AST for Vieques, Culebra, and the US Virgin Islands. Since
dangerous hot conditions will likely continue, an Excessive Heat
Watch is now in place for Wednesday. 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. Small craft should exercise caution today for
areas of the nearshore and offshore Atlantic waters due to
increasing winds. Seas up to 4 feet, occasionally up to 5 feet.
Saharan dust particles also promoting hazy conditions.

&&

.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 from 9 AM this morning to 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 from 9 AM this morning to 6 PM AST this evening
     for PRZ012-013.

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

     Heat Advisory from 9 AM this morning to 6 PM AST this evening
     for VIZ001-002.

AM...None.

&&

$$

SHORT TERM...ICP
LONG TERM....MRR