Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 090853

Area Forecast Discussion
National Weather Service San Juan PR
453 AM AST Fri Jun 9 2023


Today, expect another hot day across the local islands. The
southeasterly wind flow will prevail through the short-term
period. Saharan dust will begin to gradually diminish across the
region. At this time, no significant or heavy rain is expected
during the short-term period.


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

For Today...A mix of sunshine and partly cloudy skies will prevail
across the islands with limited shower activity expected during the
afternoon hours. Traces of suspended Saharan Dust particulates will
linger today but is to diminish and move away from the region over
the upcoming weekend. The dominant low level southeasterly wind flow
will persist with only pockets of shallow moisture expected to
affect the islands. This along with intense daytime heating may lead
to isolated to scattered shower development mainly across the
northwestern portions of Puerto Rico, in the east interior and
mainly downwind and south of the U.S Virgin Islands where hot and
sunny conditions will prevail.

Hot, humid and overall dry conditions will prevail each day through
the upcoming weekend. Recent blended satellite derived precipitable
water values were between 1.50 to 1.85 inches across the region,
suggesting a slight increase in low level moisture along with the
passing showers noted across the Caribbean waters and the Anegada
passage. A weak tropical wave is expected to pass well south of the
islands later today through Saturday, but still no significant
moisture transport and impacts are anticipated with this feature
across the islands. Therefore expect brief passing showers to
affect the coastal waters and south and east coastal areas due the
overnight and early morning hours, followed by locally and
diurnally induced showers mainly over parts of northwest Puerto
Rico, with lesser activity expected elsewhere and downwind of the
U.S Virgin islands.

Main Impacts during period. Once again, the low temperatures will
will vary between the mid-60s and low 70s in mountainous regions and
upper 70s to low 80 along the coastal and in urban areas. Maximum
temperatures will be in the low to mid 90s across the coastal and
urban areas, and in the mid to upper 80s in the higher elevations of
Puerto Rico through the weekend.  Heat indices are expected to
exceed the low and mid 100 degrees Fahrenheit each day, with
Excessive Heat Warnings and Advisories likely through the weekend.
Overall rainfall activity and moisture transport is expected to be
will be suppressed and limited by the deep layered high pressure
ridge which will remain the dominant feature through the period.
Consequently shower activity if any will be focused along portions
of the south and east coastal areas during the overnight and early
morning hours, followed by limited afternoon shower development in
the northwest sections of Puerto Rico, downwind of the U.S Virgin
Islands and over the coastal waters.

The Excessive Heat Watch continues in effect for Puerto Rico,
particularly in the coastal and urban areas of northern Puerto Rico.
The high humidity and air temperatures will cause a continuation of
the hot and sticky weather conditions, with maximum heat indices
ranging from 105 to 115 degrees Fahrenheit or more in isolated areas
along the north coastal area of Puerto Rico. The U.S. Virgin Islands
may also experience another hot day with possible maximum heat
indices ranging from 102 to 105 degrees Fahrenheit especially the
island of St Croix.

An Excessive Heat Watch will now remain in effect until Sunday
afternoon across much of Puerto Rico, including Culebra and Vieques
and Portions of the U.s. Virgin Islands.


.LONG TERM...Monday through Saturday...

This forecast period remains unchanged. Latest model guidance
continues to suggest moderate to locally fresh southeasterly winds
around 15 to 20 knots through the end of the weekend. This wind
flow is associated with a high-pressure system at all levels of
the atmosphere. This pattern will maintain unfavorable conditions
for rain development as the subsidence from the high pressure
promotes dry air above 850 mb. By the beginning of the workweek,
winds will become easterly as the high pressure repositions
slightly to the west of the forecast area. This wind shift will
bring a slight relief in the warm temperatures pattern and the
heat indices that people across Puerto Rico, Vieques, Culebra, and
the U.S. Virgin Islands have been experiencing. Nonetheless, heat
indices in the low areas will remain above 108, especially along
the northern sections of Puerto Rico.

At this time, Tuesday into mid-week continues to be the day when
the weather conditions will change slightly. This change is due
to an area of enhanced moisture that will detach from an old frontal
boundary and merge with a tropical wave heading into the forecast
area. The combination of these two weather features will increase
cloudiness and the chance for afternoon convection across the
western quadrant of Puerto Rico and morning activity across the
eastern part of the island. We anticipate moderate rainfall
amounts across the local islands. Nonetheless, expect the dry
pattern to return by the end of the workweek. Last but not least,
low concentrations of Saharan dust will be embedded in the wind
flow bringing hazy skies by the end of the period.


.AVIATION...VFR conditions will continue. SFC wnds calm to
lgt/variable overnight, bcmg fm ESE-SE at 10-15 kt with ocnly hir
gusts aft 09/14Z. L/LVL wnds fm SE 15-20 kts BLO FL180. Few
-SHRA/SHRA may affect the regional waters btw E PR and USVI and
the surrounding Caribbean waters south of PR durg prd but no
significant wx impacts fcst at local terminals durg prd. Wdly SCT
lyrs nr FL022...FL040... mstly SKC ABV.


.MARINE...Calm marine conditions will persist with seas at 4 feet
or less across most of the local waters. Seas are reaching the
Atlantic waters from the ENE. Expect the moderate to locally fresh
southeasterly winds to prevail across the region.


PR...Excessive Heat Warning from 10 AM this morning to 5 PM AST this
     afternoon for PRZ001-005-008-010-012.

     Excessive Heat Watch from this afternoon through Sunday
     afternoon for PRZ001>013.

     Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ002-004-007-011.

VI...Excessive Heat Watch from this afternoon through Sunday
     afternoon for VIZ002.

     Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for VIZ002.



LONG TERM....MMC is the U.S. government's official web portal to all federal, state and local government web resources and services.