413
FXCA62 TJSJ 220935
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
535 AM AST Fri Nov 22 2024

.SYNOPSIS...

The drier weather is about to come to an end as a line of showers
now approaching the southern boundary of our forecast area signals
the entry of a moist air mass. Temperatures will rise a little
today and remain warm tomorrow, but additional showers will end
the warming trend. Showers and isolated thunderstorms are
indicated for most of the upcoming seven days.

&&

.SHORT TERM...Today through Sunday...

Another calm night was observed across the northeastern Caribbean
under clear to partly cloudy skies. Satellite and radar observations
indicated passing showers moving over eastern Puerto Rico, and over
the local Caribbean and Atlantic waters. These showers were moving
quickly, leaving minor accumulations over the area. Minimum
temperatures were in the mid to upper 70s along the coastal portions
of the islands, with few locations reaching the lower 80s.
Meanwhile, lows were in the mid 60s across the Cordillera Central.
Winds were light and gentle from the southeast.

Today, variable weather conditions will prevail as a broad moisture
field moves from the Caribbean waters into the local area. At the
low levels, a surface high pressure will continue to strengthen
over the Central Atlantic, promoting southeasterly winds. Meanwhile,
at the upper levels a polar trough is anticipated to exit the
eastern coast of the U.S. today and will continue to move
eastwards for the next few days. As both of these features
migrate in the Atlantic, abundant tropical moisture will move
into the area promoting the development of showers and isolated
thunderstorms across the islands. The latest precipitable water
content analysis for Saturday has values between 1.7 to 2.0
inches. By Sunday, winds will shift and become from the east,
bringing additional moisture from a perturbation east of the
islands.

Prevailing winds from the southeast in combination with abundant
moisture will result in warm temperatures over the next few days.
Daytime temperatures will remain in the mid to upper 80s along the
coastal and urban areas of Puerto Rico and the U.S. Virgin Islands,
and in the upper 70s to low 80s in the Cordillera Central of Puerto
Rico. Minimum temperature will drop to the low to mid 60s in the
higher elevations, and will remain in the 70s for the rest of the
area.

.LONG TERM...Monday through Friday...

At upper levels, the sub-tropical jet over Cuba will slide just
south of the polar jet well north of the Leeward Islands, This
sub-tropical jet which will more or less coincide with the
location of a cold front will be unable to come much closer to
the area due to high pressure that stretches from the Central
Caribbean to the tropical Atlantic along 20 north. The upper level
high will drift a little south during the period.

A perturbation in the lower levels mentioned above will approach
the area and cross the Windward Islands from the east early Sunday
morning to bring additional moisture to the area. This moisture
will move quickly past the forecast area to the south and feed the
developing north-south trough north of Panama while pulling drier
air in from the east over us on Monday. As the trough develops a
low over the eastern tip of Jamaica, winds will become more
southerly and bring more moisture from the southeast Caribbean for
continued shower activity. Then on Thursday and Friday as the low
near Jamaica extends a trough to the north northeast, a trough
will brush the northern part of our forecast area as an anti-
cyclonic eddy forms off the tip of Cabo Rojo, sustaining the
modest flow of moisture across the islands.

500 mb temperatures will be mostly minus 5 to minus 6 during the
period, so there will be a chance of thunderstorms--mainly during
the afternoons over Puerto Rico and over the local waters at
night. Although some local urban and small stream flooding could
develop, showers should move just fast enough to prevent major
river rises during the period. Nevertheless most areas will have
at least some rain each day.

&&

.AVIATION...
(06 TAFs)

Mainly VFR conds are expected to prevail across all terminals during
the next 24 hrs. Aftn SHRA may result in VCSH across all the
terminals in PR and the USVI thru 22/23Z. VRB winds will continue
thru 22/14Z, then shifting and prevailing from the SE btw 8-10 kts
with land and sea breeze variations thru 22/22Z.

&&

.MARINE...Seas of 4 to 5 feet will continue in the Atlantic with
mostly northerly swell. With seas of less than 2 feet in the
shadows of the islands. Another northwest to north swell will
enter the area on Sunday and slowly decay the following Thursday
and Friday, but in the meantime small craft advisories will likely
be needed for the Atlantic waters.

&&

.BEACH FORECAST...Moderate rip current risk will prevail along the
coasts exposed to the northerly swell, but on Sunday the risk will
become high as a new swell train descends onto the northern
coasts.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.

VI...None.

AM...None.

&&

$$

SHORT TERM/AVIATION...GRS
LONG TERM/MARINE/FIRE WX...WS