795
FXCA62 TJSJ 062023
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
423 PM AST Thu Jun 6 2024

.SYNOPSIS...

A drier airmass and a Saharan Air Layer will promote hazy skies
and fair weather conditions throughout the weekend. Warm to hot
temperatures will continue to persist across the region with heat
indices surpassing the mid 100 degrees Fahrenheit. The next
tropical wave with better potential of rain is anticipated by
next Tuesday into Wednesday.

&&

.SHORT TERM...Tonight through Saturday...

A very active morning was observed over the U.S. Virgin Islands with
heavy showers and thunderstorms. Doppler radar estimated rainfall
accumulations up to 3.0 inches in St. Thomas and St. John. A
Flash Flood Warning was issued for both islands. By the early
afternoon hours, the shower activity started to move away from the
local region and weather conditions began to improve. However,
brief shallow showers were observed across the southeastern
municipalities of Puerto Rico with no significant impacts. Due to
the vast cloud coverage across the islands, daytime temperatures
remained in the mid to upper 80s. Nonetheless, heat indices were
seen in the mid to upper 100s along the coastal and urban sectors
where a Heat Advisory was in effect. Winds prevailed from the
southeast at 10 to 15 mph with sea breeze variations.

As an elongated surface trough located north of the area moves away
from the islands, a dry airmass will start to filter into the region
limiting the shower activity for the next several days. A Saharan
Air Layer will continue to arrive and spread into the islands today.
This will create hazy conditions and reduce visibilities at times.
By Friday into Saturday, limited shower activity is expected across
the region. Shower activity is possible across the northwestern
portions of Puerto Rico under the southeasterly wind flow,
available moisture, and local effects. With the arrival of the
Saharan dust particles, the suspended dust may promote the
development of strong thunderstorms with the afternoon convective
activity. Overall, mainly fair weather conditions are anticipated
for those planning outdoor activities.

Above-normal temperatures will continue across the region for the
next several days under the southeasterly wind flow. Therefore, high
temperatures in combination with the available moisture will result
in heat indices above the mid 100s each day. Therefore, a Heat
Advisory or Excessive Heat Warnings are likely over the weekend for
much of the islands.


.LONG TERM...Sunday through Thursday...

./FROM PREV DISCUSSION...Issued at 523 AM AST Thu Jun 6 2024/

A dryer and more stable weather pattern is expected to prevail
across Puerto Rico and the U.S. Virgin Islands during the
beginning of the long-term period as a deeply layered ridge sets
just east of the Leeward Islands and some Saharan Dust particles
will remain over the area. People will experience hazy skies and
sensible people with respiratory illnesses could still be
affected. The latest Precipitable Water (PW) models suggest values
decreasing to normal and even below normal climatological levels
for this time of the year, around 1.4 to 1.7 inches. Recent
guidance also shows dry air at the mid-levels of the atmosphere
and the 500 mb temperatures around -5 degrees Celsius, meaning
that if any rainfall activity does develop, it will not grow much
vertically, however, we cannot rule out the typical afternoon
convection across the islands, mainly over the western quadrant of
Puerto Rico during the afternoon hours due to diurnal heating and
local effects.

By Tuesday afternoon into Wednesday, a slight change in the weather
pattern is anticipated as patches of moisture associated with our
next tropical wave reach the island. That will result in better
chances of rain by midweek. On Thursday, a patch of dry air should
reach the islands again.

Overall, during the long term, we forecast mostly stable weather
conditions across the islands, with southeasterly to east-
southeasterly winds and moisture returning by Tuesday afternoon
into Wednesday. With this weather pattern, we anticipate warm
temperatures with the possibility that heat products like
advisories and warnings will be issued along the lower elevations
and urban areas. We encourage residents and visitors to stay
hydrated and updated with our latest weather forecasts.


&&

.AVIATION...
(18z TAFs)

Weather condition are expected to improve. However, SHRA/TSRA with
MVFR conds will remain possible across NW PR, including JBQ through
at least 06/22z. VFR conds are expected aft 06/22z at all TAF sites.
Hazy skies likely,  as suspended dust particles from the Sahara
desert filter from the east over the region, but with P6SM.

&&

.MARINE...

A surface high pressure north of the area will continue to slowly
move eastwards and build into the central Atlantic by the weekend. A
surface trough will remain mainly north and west of the area. In
response, light to locally fresh east to southeast winds will prevail
across the local waters. Isolated thunderstorms across the waters
and local passages are possible through today, then more stable
conditions are anticipated throughout the weekend. The next tropical
wave with better potential for squally weather is expected by early
next week.

&&

.BEACH FORECAST...

A low risk of rip currents across Puerto Rico, and the U.S. Virgin
Islands through the upcoming weekend. For more information and
details about the latest forecast please refer to the Surf Zone
Forecast (SRFSJU).

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001-005-008-
     010.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ002.

AM...None.
&&

$$

SHORT TERM...DSR
LONG TERM....GRS
AVIATION...OMS
PUBLIC DESK...ICP