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000
FXCA62 TJSJ 020147
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
947 PM AST Thu Jun 1 2023

.UPDATE...The latest SJU sounding indicated columnar moisture
through 700 mb, drier air aloft with a weak inversion and PWAT at
1.91 inches. This is allowing showers to grow along the southern
slopes of Puerto Rico, and are expected to continue overnight as a
moist low-level southerly wind flow prevails across the region.
Minor adjustments were made to the inherited forecast to show a
slight risk of minor flooding across southern PR tonight.
Otherwise, forecast still on track with increasing moisture and
more hot days ahead.


&&

.AVIATION...Mainly VFR conditions expected across all terminals.
However, tempo MVFR conds at TJPS are possible thru 02/06z due to
SHRA. The 02/00z TJSJ sounding indicated S-SE winds up to 22 kt
blo 3000 ft.


&&

.MARINE...Relative tranquil seas will continue during the next
several days. Latest coastal buoy data indicates seas at 2-3 feet
and southeast winds up to 13 knots.


&&

.PREV DISCUSSION... /issued 510 PM AST Thu Jun 1 2023/

SYNOPSIS...

Another hot day prevailed across Puerto Rico and the U.S. Virgin
Islands. Heat indices ranged between 108 and 117 degrees
Fahrenheit across the northern coastal and urban areas where both
the Heat Warning and Heat Advisory were in effect.This weekend
moist tropical air will arrive causing a significant increase of
rain, with Saturday through Monday looking the wettest. For the
local beaches, the rip current risk is low for the next several
days.

SHORT TERM...TONIGHT THROUGH SATURDAY...

Today, weather conditions remained stable due to a strong mid to
upper-level high pressure system over the Northeastern Caribbean.
This weather feature caused air to sink, preventing vertical
development and widespread heavy rain from forming. The surface
low pressures continue to move across the Atlantic Ocean, inducing
a southerly wind flow and gathering moisture over Puerto Rico and
the U.S. Virgin Islands. The maximum air temperature in San Juan
reached 93 degrees Fahrenheit, while Arecibo reported 95 degrees
being the highest none official observed temperature across
Puerto Rico. Daily maximums in the higher elevations fluctuated
around the 80s. This afternoon a weather observer in Hatillo
reported 116 degrees Fahrenheit. None official weather stations
reported heat indices from 108 to 117 degrees Fahrenheit in areas
where the Excessive Heat Warning and the Heat Advisory were in
effect. As anticipated, the apparent temperatures felt extremely
hot, mainly across northern municipalities. Nonetheless, during
the afternoon, brief showers developed across the northwestern and
southeastern quadrants of Puerto Rico and Culebra. This rainfall
occurred due to local effects, sea breeze variations, and
excessive heat.

Overnight, expect a similar weather pattern to prevail over Puerto
Rico and the U.S. Virgin Islands. Minimum temperatures tonight
will fluctuate around the 70s in the coastal areas and upper 60s
to low 70s in the mountains. However, some shower activity is
anticipated during the early morning hours as tropical moisture
gets dragged into the islands. By the end of this workweek into
the weekend, sufficient tropical moisture will reach the forecast
area from the south, keeping the area moist and increasing
rainfall activity in the windward sections of the islands. In the
afternoons, scattered showers are likely with some thunderstorms
due to the possible increase in instability combined with local
effects. Model guidance still indicates temperatures higher than
usual, which may result in excessive heating, especially in urban
and coastal areas. However, if widespread showers develop
throughout the day, the temperatures may cool down more than the
guidance suggests.

LONG TERM...Sunday through Thursday...FROM previous
discussion...

Low pressure across the western Atlantic continues to drive moist,
tropical air over the region due to breezy southerly flow from
the surface to 250 MB. Due to this, an increase of passing showers
across southern Puerto Rico and the local islands is expected
throughout the day. There will also be convection each afternoon
forming on the northern side of the Cordillera Central, effecting
the northern sections of Puerto Rico, including the San Juan metro
area. A robust ridge in the mid to upper-levels over the eastern
Caribbean will help to stabilize conditions, also it will help
each day become very hot as it provides sinking air. Urban and
coastal areas are expected to experience heat indices in the 110s
which can be hazardous.

This pattern will continue until Monday night when a surface high
builds to the east of the region causing a backing of the winds which
will bring drier air into the region. Shower activity during this
time will be limited due to the persistent ridging aloft and low
precipitable water values, however afternoon convection can still
produce noticeable rainfall each afternoon. Thursday in
particular looks very dry, the driest day possible for the
beginning of summer. Each day around noon time, coastal and urban
areas will experience hot temperatures, therefore stay diligent
in checking if excessive heat advisories or warnings are in
effect.

AVIATION...VFR cond expected at all terminals during the next 24
hours. Sfc wnds from the southeast at 10-15 kt, with land breeze
variations and less than 10 kts aft 01/23Z. Mstly SCT lyrs nr
FL028...FL050...SKC ABV. No sig operational wx impacts attm.

MARINE...No changes to the previous forecast. Relative tranquil
marine conditions will continue across the local waters, with
coastal buoys indicating seas below 4 feet and southeasterly
winds at 10 to 15 knots. A low risk of rip currents across all the
islands will continue.

$$

&&

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

$$

DSR/ICP