577
FXCA62 TJSJ 140945
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
517 AM AST Fri Jun 14 2024

.SYNOPSIS...

An induced surface trough passing through the region will promote
passing showers and afternoon convection, mainly across western
Puerto Rico. Isolated areas may experience heavy rainfall at times,
however mid to upper-level ridging will limit widespread rainfall. A
Heat Advisory will be in effect from 10 AM to 6 PM for the metro
area, north- central, northwestern and western PR. A limited heat
risk will still be present along the rest of the lower elevation and
coastal areas of the islands. Please continue to monitor the latest
forecast for possible updates. By tomorrow, a plume of Saharan dust
of moderare to high concentration is forecast to spread across the
region, causing hot and hazy conditions that last through the second
half of the weekend into the next workweek. An Excessive Heat Watch
is in effect for tomorrow.

&&

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

A mid to upper ridge will remain anchored across Hispaniola and
the Mona passage through the weekend while an upper trough will
continue to extend southward across the northern Leeward Islands
into the eastern Caribbean. The dominant surface high pressure
will continue across the west and central Atlantic while an
induced surface trough is forecast to cross the region today
through Saturday. This will maintain a light to moderate east
northeast wind flow this morning then become east southeast later
this afternoon then more southeasterly throughout the weekend.

Fragmented low level moisture accompanying the trough and carried
by the present wind flow will bring periods of light to moderate
showers to the local waters and mainly the windward side of the
islands during the rest of the early morning. No significant rains
are anticipated. However this slight increase in moisture along
with good daytime heating will be sufficient to increase
instability across the region resulting in afternoon convection
particularly across the central interior and west sections of
Puerto Rico. Isolated areas may experience periods of locally
heavy rains with the afternoon thunderstorms, however the mid to
upper-level ridging will continue to limit widespread rainfall.
Hot and humid conditions are expected to persist today with
maximum heat indices to reach the 100 degrees along some coastal
and urban areas resulting in excessive heat impacts.

By late Saturday and through Sunday, a plume of Saharan dust of
moderare to high concentration is forecast to spread across the
region while the low level winds becomes southeasterly. With this
expected warm and humid southerly flow, expect continued hot and
hazy conditions. The combination of suspended Saharan dust
particulates and the mid to upper level ridging will favor
subsidence and good compression of the warm air in the low layer.
Daytime high temperatures will be in the low 90s especially along
the north and west coastal areas with maximum heat indices
expected to again exceed 100 degrees, resulting in excessive heat
impacts particularly along the west north and east coastal and
urban areas. Late afternoon convection will be likely each day but
excessive and widespread rainfall is not forecast for the period.

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

Although a decrease in saharan dust is forecast to start the
workweek, another pulse will continue to promote hazy conditions
through most of the long term period. Current model guidance
suggest Precipitable Water (PWAT) values at generally normal
values to start the period with a patch of below normal PWAT
values reaching the area on Tuesday. For Wednesday and Thursday,
columnar moisture will increase once again to normal to above
normal values as moisture related to a surface trough and a
possible wave, although uncertainty remains. A developing upper
level trough near the area will also increase instability. Although
model guidance suggest moisture over the mid levels, a more
notable increase is suggested by Wednesday. Most available
moisture to start the workweek will remain below 850 mb,
however. East to east- southeast surface winds should affect the
islands through Thursday, when they become more easterly and
increase. This will steer warmer tropical air towards the islands,
promoting overall warm to hot conditions. Heat related products
will possibly be issued for the islands to start the period. 925
mb temperatures are forecast to be above normal to start the
workweek.

&&

.AVIATION...

(06Z TAFS)

Prevailing VFR across the area except for SHRA/Isold TSRA dvlpg
aft 14/17Z ovr ctrl interior and wrn sections of PR till 23Z. SFC
wnd fm northeast less than 10 kts bcmg fm east northeast 10-15 kt
with gusts to nr 20kt along with sea breeze variations. Isold SHRA
mainly ovr the regional waters en route btw islands. SHRA/iSLD
TSRA psbl nr TJBQ/TJMZ/TJPS with FEW -SHRA psbl vcty of USVI
terminals fm 14/18Z- 23Z.

&&

.MARINE...

Surface high pressure over the Atlantic and an induced trough now
just east of the area will promote light to moderate east
northeast winds this morning then become more southeasterly later
this afternoon. Moisture remnants steered by the northeast
windflow and enhanced by an upper level trough just east of the
area will increase the potential for showers and isolated
thunderstorms development over portions of the local waters the
rest of today. Winds will continue to diminish and veer, becoming
east southeast then southeast through the weekend with increasing
Saharan dust expected across the region through Sunday.

&&

.BEACH FORECAST...

The risk for rip currents is low, however, life-threatening rip
currents often occur in the vicinity of groins, jetties, reefs,
and piers.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 6 PM AST this evening
     for PRZ001-005-008-010.

     Excessive Heat Watch from Saturday morning through Saturday
     afternoon for PRZ001-002-005-008-010-012-013.

VI...Excessive Heat Watch from Saturday morning through Saturday
     afternoon for VIZ001-002.

AM...None.

&&

$$

SHORT TERM...RAM
LONG TERM....MRR