Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 182045
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
445 PM AST Mon Mar 18 2024

.SYNOPSIS...

A surface high pressure moving towards the eastern Atlantic will
continue to promote breezy conditions across the islands. Dry and
fair weather conditions will continue to persist until mid-week.
However, an increase in shower frequency is expected from
Wednesday onwards due to the arrival of a cold front and its
associated frontal boundary. Warmer temperatures are anticipated
this week as surface winds prevails from the southeast.

&&

.SHORT TERM...Tonight through Wednesday

Mostly clear skies prevailed across the local region today. Few
clouds were seen streaming off the islands and over the Cordillera
Central. However, little or none precipitation was observed. Warm
temperatures were registered today across the islands. The Luis
Munoz Marin Int. Airport in San Juan registered a maximum
temperature of 91 degrees Fahrenheit, just 3 degrees below the
record for today. Overall, temperatures remained in the upper 80s
and low 90s across the coastal and urban areas of Puerto Rico and
the U.S. Virgin Islands. Heat indices reached the mid 100s in the
municipalities of north central Puerto Rico. Winds prevailed from
the east southeast from 15 to 20 mph, with higher gusts.

A surface high pressure continues to dominate the local weather
promoting fair weather conditions. However, passing showers dragged
by the trade winds cannot be ruled out. By Tuesday, as the surface
high moves towards the eastern Atlantic winds will veer from the
south southeast. Dry and fair weather conditions will persist with
warmer-than-normal temperatures, especially across the north central
portions of Puerto Rico and portions of St. Croix. Daytime
temperatures will remain in the upper 80s to low 90s across the
urban and coastal areas of the islands. Heat indices will stay above
the 100s across these areas. From Wednesday onwards, an increase in
moisture is expected due to the approach of a cold front and its
associated frontal boundary. Therefore, expect an increase in the
frequency of passing showers during the morning hours, followed
by afternoon showers across the central and western portions of
Puerto Rico and the U.S. Virgin Islands. Some of this activity
could lead to ponding of water on roads and in poor drainage
areas.

&&

.LONG TERM...Thursday through Monday...

./FROM PREV DISCUSSION...Issued at 434 AM AST Mon Mar 18 2024/

A weak frontal boundary moving southeastward in the western Atlantic
will begin to pass through the region on Thursday, causing a backing
of the surface winds to more of a northeasterly direction and a
noticeable increase of moisture content moving over the islands
by Friday morning. This shifting of the winds and increase of
precipitable water will bring a wetter pattern with scattered
showers across eastern Puerto Rico and the USVI during the morning
hours followed by afternoon convection across western Puerto
Rico.

On Friday, a surface low begins to develop in the Gulf of Mexico,
migrating into the western Atlantic as it moves along the eastern
coastline of the US meanwhile displaying nor`easter characteristics.
Eastward of this system a strong surface ridge will direct a moist
easterly flow locally through Saturday which will continue the
pattern of an abundance of passing showers with afternoon
convection, with the heaviest rainfall over western Puerto Rico
during the afternoon.

By Sunday the potential nor`easter would of moved into the upper
western Atlantic and a Rossby wave trough develops to the
southwest, positioning north of the region by Monday morning. The
presence of this will cause a veering in the surface winds to a
southeasterly direction on Sunday, becoming southerly and variable
Monday onward. During this time precipitable water values spike
as this long wave pattern brings a moist airmass and unstable
conditions over the eastern Caribbean. This may bring a
significant increase of rainfall across the islands for multiple
areas, however model guidance is subject to change so stay tuned.

&&

.AVIATION...
(18Z TAFS)

ESE flow is prevailing over the local area with some sea breeze
influences and winds of 8-18 kts with hir gusts--the strongest have
been nr TJPS so far. Winds will bcm land breezes btwn 18/23-19/12Z
then return to today`s flow. VFR conds to prevail but brief MVFR
expected in NW PR btwn 18/18-21Z and again fm 19/18-21Z, not
necessarily at TJBQ terminal. Max winds W 85-95 kts btwn FL400-470.

&&

.MARINE...

A broad surface high pressure moving into the central and eastern
Atlantic will continue to promote moderate to locally fresh trade
winds through mid-week, resulting in choppy seas. Winds will slow
down by Tuesday and Wednesday, resulting in subsiding seas and calm
conditions across the local waters.

&&

.BEACH FORECAST...

Breezy conditions will continue to promote a moderate rip current
risk along the northern beaches of Puerto Rico, Culebra, the
northern U.S. Virgin Islands, and St. Croix. The protected waters
of west and southern Puerto Rico and Vieques remain under a low
risk. The rip current risk is expected to remain moderate until
mid-week, when the risk of rip currents becomes low across all the
local beaches.

Rip currents are powerful channels of water flowing quickly away
from shore, which occur most often at low spots or breaks in the
sandbar and in the vicinity of structures such as groins, jetties
and piers. Heed the advice of lifeguards, beach patrol flags and
signs. If you become caught in a rip current, yell for help.
Remain calm, do not exhaust yourself and stay afloat while waiting
for help. If you have to swim out of a rip current, swim parallel
to shore and back toward the beach when possible. Do not attempt
to swim directly against a rip current as you will tire quickly.
If you do not know how to swim, we advise you to stay out of the
ocean.


&&

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

$$

SHORT TERM...DSR
LONG TERM....GRS
AVIATION...WS
PUBLIC DESK...RVT


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