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National Weather Service Forecast for: San Juan, Puerto Rico  


National Weather Service Forecast Details


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GRLevel3 radar from NWS station TJUA

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Day 2 rainfall

Day 3 rainfall

FXCA62 TJSJ 022042

Area Forecast Discussion
National Weather Service San Juan PR
442 PM AST Sat Dec 2 2023

Mostly fair weather will prevail across the region tonight, with
a slight chance of isolated to scattered showers at times. This
seasonal pattern will continue throughout the weekend onward.
The combination of a northerly swell and the increasing
winds will maintain choppy to hazardous seas across the offshore
waters and local passages through at least tomorrow. The risk of
rip currents remains high for northern and eastern facing beaches.


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

Mainly fair weather conditions were observed during the morning
hours and early afternoon. Despite the approaching weak frontal
boundary from the north, shower activity was limited with some
increase in cloud coverage in some areas. For this reason, POPs were
slightly reduced for the afternoon hours.

For the rest of the afternoon and evening, expect an increase in
cloud coverage and possibly isolated to scattered showers over the
Atlantic waters being pushed southward over the local area as the
frontal boundary continues to sink. This pattern will continue
through early tomorrow. Significant rainfall accumulations are not
expected since ridging aloft will continue to inhibit convective
activity across the northeastern Caribbean.

For the rest of the short-term period, model guidance has been very
consistent in the deepening of a short-wave trough at upper levels,
pushing the mid-level ridge westward. However, the latest model runs
are maintaining a greater portion of the mid-level ridge over the
local islands compared to previous model cycles. This will cause 500
mb temperatures to not drop as much with 250mb heights and 1000-500
mb thicknesses momentarily dropping, but increasing rapidly to above-
normal levels. Therefore, any shower development in the coming days
will remain shallow.

That said, the deepening upper-level short-wave trough east of the
Leeward Islands will induce a series of surface perturbations that
will be dragged by the easterly trades. Therefore, periods of fair
weather conditions with some shower activity along with an increase
in cloud coverage can be expected. The frequency of showers and
areas affected will be modulated by the arrival of these surface
perturbations along with surges of moisture and variations in the
steering wind flow. This is a very typical weather pattern for the
season. At most, we can expect hazardous driving conditions for
short periods.


.LONG TERM...Tuesday through Saturday...
/from previous discussion/

A seasonal weather pattern will persist for most of the long
term. Model guidance continues to suggest the development of a
Tropospheric Upper-Level Trough just east of the Leeward Islands
by the beginning of the upcoming workweek. Although the islands
will remain on the subsidence side of the TUTT, a weak induced
surface trough from the TUTT above will result in trapped moisture
at 800 mb. The shallow moisture embedded in the east-
southeasterly winds and the local effects will be enough to
increase the frequency of the passing showers across windward
sections on Tuesday into Thursday. By late Wednesday into
Thursday, the high surface pressure over the central Atlantic will
be the main feature, resulting in east-southeast wind, bringing
pulses of moisture. Global model guidance suggests a surface wind
variation due to the arrival of a pre-frontal trough moving
southward into the Caribbean for the last part of the long-term


.AVIATION...VFR conds durg prd. VCSH and brief SHRA is expected
through the period at least across TJBQ/TJSJ/TIST as a weak frontal
boundary sinks southward. ENE winds will continue at 12-20 kts with
higher gusts and sea breeze variations thru at least 21z, then
decreasing blo 10 kt with occasional higher gusts near SHRA.



A broad surface high pressure building over the western Atlantic
will promote moderate to fresh easterly winds across the regional
waters. The combination of a northerly swell and the increasing
winds will maintain choppy to hazardous seas across the offshore
waters and local passages through at least tomorrow. Therefore, a
Small Craft Advisory is in effect for the offshore Atlantic waters
until at least 8 PM on Monday. For beachgoers, there is a high
risk of rip currents across the northern sections of Puerto Rico
and the USVI tonight.


PR...High Rip Current Risk through Sunday afternoon for PRZ001-002-

     High Rip Current Risk through late tonight for PRZ012.

VI...High Rip Current Risk through late tonight for VIZ001.

AM...Small Craft Advisory until 8 PM AST Monday for AMZ711.




NWS SJU Office Area Forecast Discussion

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Wind Shear Tendency

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Sea Surface Temperatures Anomalies