Excessive Heat Warning 9, NWS JSJ

Area Forecast Discussion
National Weather Service San Juan PR
928 PM AST Wed Jun 7 2023

...New UPDATE, AVIATION, MARINE...

.UPDATE...
Issued at 917 PM AST Wed Jun 7 2023

Throughout the night, the heat index will vary between the mid-70s
and 80s in mountainous regions, while coastal and urban areas will
experience temperatures ranging from the low to upper 80s. Mid to
upper-level high pressures currently prevent rainfall in Puerto
Rico and the U.S. Virgin Islands. However, there is a chance of
one or two rain showers in the windward areas due to a patch of
moisture. The high humidity and air temperatures will cause a
continuation of the hot weather tomorrow, resulting in heat index
values ranging from 105 to 115 degrees Fahrenheit or more. As a
result, an Excessive Heat Watch has been issued for Puerto Rico,
particularly in the coastal and urban areas of northern Puerto
Rico. The U.S. Virgin Islands may also experience a hot day with
heat indexes ranging from 102 to 107 degrees Fahrenheit.

&&

.AVIATION...
(00Z TAFS)
Issued at 917 PM AST Wed Jun 7 2023

VFR conditions will persist with somewhat hazy skies but with VIS
greater than 6SM. Expect calm to variable winds overnight (thru
08/13z), when will return from the ESE/SE at 10-15 kt with gusty
winds. A few showers may affect E-PR/USVI and the surrounding
waters without significant impacts tomorrow.

&&

.MARINE...
Issued at 917 PM AST Wed Jun 7 2023

Calm marine conditions will persist with seas at 4 feet or less
across most of the region. Seas are reaching the Atlantic waters
from the NNW with an average period of 6.8 seconds. At the same
time, the seas across the Caribbean are arriving from the SE with
a 5.7 seconds period.

&&

.SYNOPSIS...Excessive heat conditions will persist until the
weekend across Puerto Rico and the U.S. Virgin Islands. Hazy
skies due to Saharan dust particles will continue to gradually
decrease through the workweek. No significant rains are expected
for the next coming days. A Heat Watch is now in effect for Puerto
Rico until Saturday afternoon.

&&

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

Relatively dry conditions persisted, once again, across Puerto Rico
and the U.S Virgin Islands. Saharan Dust continue to be present
across our skies, but it will gradually diminish in concentration
the rest of the workweek. No precipitation was observed by the
local Doppler radar. Maximum temperatures stayed in the low to mid
90s across the coastal and urban areas of the islands and in the
mid to upper 80s across the Central Cordillera. The temperature at
the Luis Munoz Marin International Airport was 94 degrees, which
ties an old record of 94 degrees Fahrenheit for a June 7th. An
Excessive Heat Warning was in effect for the north-central
portions of Puerto Rico, where the heat indices fluctuated between
103 to 119 degrees Fahrenheit. The U.S. Virgin Islands reported
heat indices over 100 degrees. A Heat Watch is now in effect until
the weekend for Puerto Rico, including Culebra and Vieques.
Another warm day in the northeastern Caribbean.

As a surface high pressure in the central Atlantic moves towards the
east, the wind flow will become from the southeast. This is expected
to increase the cloud coverage across the region, with limited
shower activity anticipated. However, dry and warm conditions will
persist until the beginning of next week. The Precipitable Water
content Analysis (PWAT) values show values up to around 1.35
inches, gradually decreasing to around 1.20 inches. No big changes
for the short-term forecast are expected. The probability of
precipitation remains low. The Excessive Heat Warning and the Heat
Advisory for the north-central and western Puerto Rico remain in
effect until 5 PM AST. Temperatures will persist in the low to mid
90s across the coastal and urban areas, and in the mid to upper
80s across the mountains for the rest of the workweek. Heat
indices are expected to exceed the low and mid 100 degrees
Fahrenheit everyday, and Excessive Heat Warnings and Advisories
are likely.

&&

.LONG TERM...Saturday through Thursday...

High pressure at all levels will continue to drive east southeast
winds at 15 to 20 knots throughout the weekend. Unfavorable
conditions for rain formation are expected to continue as the high
promotes dry air above 850 mb. By Monday, the high reposition a
little to the west and the winds will back from the east. This
chance in winds is expected to bring a slight relief to the
intense temperatures and heat indices that have been experienced
across the islands. However, the heat indices are still expected
to remain above 108 along some sections of northern Puerto Rico.

By late Monday and Tuesday, an area of enhanced moisture detached
from an old frontal boundary is expected to reach the islands,
increasing cloudiness and the frequency of showers. So far, this
feature is expected to only bring moderate rainfall amounts. Then,
the northern-most moisture field of a tropical wave will also
bring some moisture over the islands, with a few more showers
anticipated. Low concentrations of Saharan dust will be embedded
in the wind flow by the end of the period, with hazy skies
possible.

&&

.AVIATION...Mainly VFR conds are expected across all terminals. HZ due to
Saharan dust will cont but VIS will be greater than 8SM. Generally
SEly winds will be at 10-15 kts with higher gusts. Winds will
diminish to less than 10 kt aft 07/23Z. Some sea breeze intrusion on
the NW coasts. Aft 08/10Z isold SHRA SE coast PR  and local Carib
waters, winds incrg to 10-15 kt by 08/14Z. Maximum winds SE 17-22 kt
btwn FL026-060.

&&

.MARINE...Mariners can expect seas of 4 feet or less across the
local waters. Winds will remain from the southeast at 10 to 15
knots, causing choppy seas next Sunday. The risk of life-
threatening rip currents remains low across all beaches of the
local islands.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Excessive Heat Watch through Saturday afternoon for PRZ001>013.

VI...None.
AM...None.
&&

SHORT TERM...CAM
LONG TERM....GRS
AVIATION...CVB