374
FXCA62 TJSJ 070900
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Fri Jun 7 2024

.SYNOPSIS...

A Saharan Air Layer and drier airmass will continue to promote
hazy skies throughout the weekend. Generally, fair weather
conditions are expected, however shower activity and some
thunderstorms may develop across northwestern portions of Puerto
Rico during the afternoon hours due to local effects. 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...Today through Sunday...

A Saharan Air Layer and a mid-level ridge promoted stable weather
conditions across the islands overnight. Mid to upper-level clouds
moved across the islands, dissipating early this morning. The
minimum temperatures were warmer than the climatological values of
PR and the USVI, while surface winds continued from the southeast.

Today will begin warmer than normal. The available moisture and the
southeasterly wind flow will result in warm to hot conditions across
Puerto Rico and the U.S. Virgin Islands. This stable weather pattern
with little or no rain will intensify the hot spell, potentially
extending into the weekend. It`s crucial to note that an Excessive
Heat Warning (NPWSJU) is in effect for the urban and coastal areas
of mainland PR and St Croix, while Culebra, Vieques, St John, and St
Thomas have a Heat Advisory today. This information is vital for
your safety and well-being, especially for the most vulnerable
communities like pregnant, newborns, children, elderly, chronic
illness patients, and pets. An Excessive Heat Watch is also in
effect for Saturday, between 9 AM AST and 6 PM AST, due to the high
chance of observing dangerous hot heat indices across the urban and
coastal areas.

Even though the ridge pattern in the upper atmosphere and the
presence of a Saharan Air Layer will restrict rain activity, local
factors could lead to isolated to scattered afternoon convection
each day. Additionally, patches of clouds moving in along the
windward areas may bring brief passing showers during the day.
Nighttime showers could form over the nearby waters, occasionally
moving inland due to the warmer-than-usual sea surface temperatures.

The bulk of a tropical wave`s moisture is forecast to move far to
the south across the Caribbean Sea late Sunday night into Monday.
However, its perispheric moisture field could increase the frequency
or intensity of the showers across the regional waters from late
Sunday night into early Monday morning.

&&

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

The drier and more stable weather pattern is expected to prevail
across Puerto Rico and the U.S. Virgin Islands during the
beginning of the work week due to the presence of a drier airmass
and a mid to upper level high-pressure ridging over the area. The
latest Precipitable Water (PW) models suggest values decreasing
to around 1.4 to 1.7 inches on Monday, which is normal to even
below normal climatological levels for this time of the year.
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. 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. The 925 mb temperatures should remain well above
normal through early next week. That could promote hazardous heat
conditions, particularly across coastal and urban areas. Therefore,
heat products will likely need to be issued until next week. We
encourage residents and visitors to stay hydrated and updated with
our latest weather forecasts.

We foresee a change in the weather pattern to begin next Tuesday
into Wednesday as patches of moisture associated with a tropical
wave that will move to our south reach the island. That will
result in better chances of rain by midweek onwards. At the end of
the week, models agree that additional moisture from another
surface disturbance will also reach the island and further enhance
the chance of showers.

&&

.AVIATION...
(06TAFs)

VFR conditions will prevail today with traces of suspended
Saharan desert particles. Winds will continue from the SE at 6 kt
or less through 7/13z when they range around 10-15 kt, but with
higher gusts due to sea breeze variations. Strong SHRA could
develop during the afternoon near the vicinity of JBQ, especially
7/20z-8/00z.

&&

.MARINE...

A surface high pressure north of the area will continue to move
eastwards into the central Atlantic promoting light to moderate east
to southeast through most of the forecast period. More stable
conditions are anticipated throughout the weekend, then the next
tropical wave with better potential for showers and isolated
thunderstorms possible across the waters and local passages is
expected by early next week.

&&

BEACH FORECAST...

A low risk of rip currents across most beaches of Puerto Rico and
the U.S. Virgin Islands through early next week, then low to
moderate risk is anticipated with an approaching tropical wave by
midweek onwards. For more information and details about the
latest forecast please refer to the Surf Zone Forecast (SRFSJU).

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Excessive Heat Warning from 9 AM this morning to 6 PM AST this
     evening for PRZ001>003-005-007-008-010-011.

     Excessive Heat Watch from Saturday morning through Saturday
     afternoon for PRZ001>003-005-007-008-010>013.

     Heat Advisory from 9 AM this morning to 6 PM AST this evening
     for PRZ012-013.

VI...Excessive Heat Warning from 9 AM this morning to 6 PM AST this
     evening for VIZ002.

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

     Heat Advisory from 9 AM this morning to 6 PM AST this evening
     for VIZ001.

AM...None.


&&

$$

SHORT TERM/AVIATION...CAM
LONG TERM/MARINE/BEACH FORECAST...YZR