National Weather Service San Juan PR
500 AM AST Thu Nov 3 2022
.SYNOPSIS...
A mixture of sunshine and clouds will prevail today. However, a
weak tropical wave will promote afternoon convection across the
interior and western sections of Puerto Rico, near the San Juan
Metro Area and downwind from the USVI. A polar trough approaching
from the west will promote an unstable and wet pattern Friday
through early next week. Therefore, special attention to the
forecast for this event is advised as it evolves during the next
few days.
&&
.SHORT TERM...Today through Saturday...
Ridging aloft is slightly being pushed by a polar trough that is
starting to strengthen and descend from the Eastern Seaboard;
however, drier air above the 600 mb layer will persist throughout
the day inhibiting somewhat the effects of ridge erosion at upper-
levels. At lower-levels, GOES-16 Total Precipitable Water
estimates values between 1.5 to 1.6 inches over the forecast area
which is below normal to near normal climatological levels for
this time of year and is expected to remain within these values
today. Therefore, under an east southeast steering wind flow, a
seasonal weather pattern is expected during the day with advective
showers affecting the windward coastal areas of the local islands
during the morning hours and diurnally induced afternoon showers
and isolated thunderstorms developing across the Cordillera
Central and western/northwestern Puerto Rico. The San Juan metro
area could observe heavy showers and brief isolated thunderstorms
in the afternoon as well. Streamers downwind of the smaller
islands can be expected with some brushing eastern portions of
Puerto Rico at times. Urban and small stream flooding can be
observed with this activity. Localized flash floods cannot be
ruled out.
By Thursday evening and onwards, weather conditions will gradually
deteriorate through the weekend as a complex pattern unfolds. First
the leading edge of a tropical wave, currently located over 63W,
will start to filter in the evening hours. As it moves westward, the
tropical wave will pass mostly south, but will increase moisture
content across the CWA throughout Friday. Instability aloft will
also gradually increase as the aforementioned polar trough continues
to sink in and settles northwest of the area. Dynamics aloft will
become favorable as cold air advection and a divergent pattern
establishes over the northeastern Caribbean. At low-levels, a broad
area of low pressure will start to develop west of the area inducing
a southerly flow by Friday evening. This deep-layer trough will
interact with the tropical wave and even pull additional deep
tropical moisture from the south by Friday night into Saturday.
Uncertainty remains regarding the area of maximum moisture
convergence, but models have been consistent that southeastern
Puerto Rico, Vieques, Culebra and U.S. Virgin Islands will be most
impacted by this weather pattern, with Saturday being the most
active day.
With this set up, a more enhanced convective pattern can be expected
on Friday as high moisture content and instability interacts with
surface heating during the day. The area of heaviest rain will
gradually increase with numerous showers and scattered thunderstorms
developing over interior and northwestern quadrant of Puerto Rico.
Convective activity will become widespread by Friday evening and
overnight hours. For now, model guidance has most of the activity
slowly moving eastward by early Saturday through the end of the
short-term period. However, this will all depend on where the area
of maximum convergence develops. Therefore, continue to monitor the
evolution of this forecast as this event has the potential of
causing widespread thunderstorm activity capable of producing gusty
winds and heavy rain over already saturated soils, rapid river rises
and mudslide events.
&&
.LONG TERM...Sunday through Thursday...
Model guidance, once again, indicated unsettled weather
conditions from Friday (from the Short Term Period) through early
next week associated with a strong TUTT-Low lingering through late
Monday night. The confidence remains low-moderate concerning the
exact location where the rainfall maxima will occur as the ECMWF
and GFS continue flip-flopping around it. Both models suggest that
the southern and eastern sections of Puerto Rico, the U.S. Virgin
Islands, and surrounding waters have the highest potential to
observe the maximum precipitation amounts. In addition, the
National Hurricane Center (NHC) continues to closely monitor the
evolution of this event as the broad area of low pressure that
might develop in the vicinity has a low chance of tropical cyclone
formation in the next five days (20 percent). Please refer to the
latest Tropical Weather Outlook (TWOAT) issued by the NHC.
Tuesday through Thursday may be a transition period, exiting the
wet and unstable weather pattern. However, this part of the
forecast will be tight to the evolution of the area of low
pressure, which NHC is monitoring. This system could alter the
wind pattern (inducing a southerly wind flow) and may continue to
lift plenty of tropical moisture from the southeastern Caribbean
over the islands (Northeast Caribbean). Now, model guidance is
leaning toward continuing a wet and showery weather pattern
through next week's second part, pushing the plume of moisture
over the Northeast Caribbean. The confidence is still low because
it will depend on the trajectory of the moisture plume.
&&
.AVIATION...
(06Z TAFS)
VFR conditions will prevail. SHRA will affect USVI
terminals without significant impacts. Local effects will aid in the
formation of SHRA/TSRA between 03/16-22z across the interior and
western PR and downwind from El Yunque and the USVI. This activity
may affect JPS/JBQ/JSJ. Expect calm to light and variable winds thru
03/13z, and then they will return from the ESE at around 10-15kt
with sea breeze variations.
&&
.MARINE...
A small northerly swell will continue to fade across the local
waters slowly. Seas will continue up to 4 feet, and the winds out
from the east at 10 to 15 knots. However, local effects could
locally increase winds and seas each afternoon.
A tropical wave today and an upper-level trough Friday through
the early next week will deteriorate weather conditions across
the northeast Caribbean. Unsettled weather and the arrival of
another northerly swell will cause marine and coastal conditions
to deteriorate over the weekend.
For beachgoers, the risk of rip currents is moderate along the
Atlantic Coastline of Puerto Rico, Vieques, Culebra, and the
Virgin Islands. The risk of rip currents will increase to high
this weekend into early next week for most of the beaches.
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
&&
$$
SHORT TERM...CVB
LONG TERM....CAM