458
FXCA62 TJSJ 092048
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
448 PM AST Sat Nov 9 2024

.SYNOPSIS...

Unstable and wet conditions will continue for the next few days
as a passing tropical wave moves across the region. Moderate to
heavy showers and strong thunderstorms are expected to affect the
region through Sunday evening, resulting in a elevated to
significant rainfall risk. Some of the expected hazards, include:
urban and small stream flooding, quick river rises, mudslides and
flash flooding. Therefore, a Flash Flood Watch remains in effect
for the local islands through Sunday evening.

&&

.SHORT TERM...Tonight through Monday...

Variable weather conditions prevailed over the local islands today,
with limited to moderate showers across the eastern portions of
Puerto Rico and the U.S. Virgin Islands. In the afternoon, moderate
to heavy showers and isolated thunderstorms were observed across the
interior and western portions of Puerto Rico. Doppler radar
estimated between 2.0 to 3.0 inches of rain across these areas, with
the highest accumulations between Las Marias and Moca. Several Flood
Advisories were issued for the aforementioned areas. Overall,
highs remained in the mid to upper 80s along the coastal and urban
areas, and in the upper 70s to low 80s in the mountains.

Weather conditions will become more unstable overnight as a passing
tropical wave brings additional moisture into the area. The latest
precipitable water guidance has values up to 2.5 inches, suggesting
above-than-normal moisture across the region. Overnight, moderate to
heavy showers and strong thunderstorms will result in an elevated to
significant risk of excessive rainfall, mainly over eastern
Puerto Rico and the U.S. Virgin Islands. These conditions will
persist on Sunday, enhancing the potential for more showers and
thunderstorms across the region.

The tropical wave should depart the region by Sunday evening into
Monday, improving conditions across the islands. Nonetheless,
lingering moisture from the tropical wave in combination with
daytime heating and local effects will promote the formation of
additional activity mainly over the western municipalities of Puerto
Rico.

A Flash Flood Watch remains in effect through Sunday evening, with
potential impacts ranging from urban and small stream flooding to
flash and river flooding, especially in saturated areas. Residents
and visitors should monitor conditions closely and stay informed of
any guidance from local authorities.


.LONG TERM...Tuesday through Saturday...

/FROM PREV DISCUSSION...Issued at 513 AM AST Sat Nov 9 2024/

For the long term, variable weather conditions will prevail as mid
to upper-level ridges hold for most of the period, providing
stable conditions. Although drier intrusion at the mid to upper
level will remain in place for Wednesday, tropical moisture
trapped in the lower levels will reach the islands driven by the
east-southeast winds resulting from the interaction of a broad
surface high pressure over the Central Atlantic and a frontal
boundary and the associate low pressure sinking southeastward. This
change in the surface will induce a more east-southeast across
the islands. Under this pattern for Wednesday, a drier airmass
will reach the islands, limiting the widespread shower activity.

Stable conditions will not last much, and by Thursday, the
approach of moisture from a frontal boundary and a change in the
surface winds will enhance the showery pattern across the islands
again. Although the moisture from this feature moves near and over
the region on early Thursday, good convection is forecast for the
afternoon hours across the northeastern section of the islands
due to the northeast wind flow dominating the area. By Friday into
Saturday, as the global model guidance suggested, after the
Frontal Passage (FROPA), much drier air will dominate the pattern
with less shower activity and much colder temperatures.


&&

.AVIATION...
(18Z TAFs)

SHRA/TSRA dvlpd ovr wrn/nwrn PR and will cont till arnd 10/00Z. MVFR
conds with mtn obscurations there. Elsewhere VFR conds but with mtn
topping in -RA.  S of the FA TSRA with tops to FL500 are movg slowly
NW as they weaken. Some of these will mov ovr PR/USVI aft 10/02Z.
Sfc winds were E-SE 6-12 kts with sea breeze influences. These are
expected to continue mostly SE overnight. Max winds SW 25-30 kts
btwn FL430-480.

&&

.MARINE...

Light to moderate winds from the east southeast will prevail as a
surface trough moves across region for today into Sunday, increasing
on Monday after the passage of a tropical wave. An upcoming tropical
wave will result in an increase of shower and thunderstorm activity
resulting in localized hazardous marine conditions during the
weekend.

&&

.BEACH FORECAST...

There is a moderate to low risk of rip current across all the
exposed beaches of Puerto Rico and the U.S. Virgin Islands through
Sunday evening. For Monday, the risk of rip current will become
high for PR`s northern coast. Although conditions might be
suitable for visiting the beaches, an increase in thunderstorms
might result in hazardous coastal conditions across the islands
until Sunday evening.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Flood Watch through Sunday evening for PRZ001>013.

VI...Flood Watch through Sunday evening for VIZ001-002.

AM...None.
&&

$$

SHORT TERM...CAM
LONG TERM....GRS
AVIATION...WS
PUBLIC DESK...MMC