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FXCA62 TJSJ 292058 AFDSJU

Area Forecast Discussion National Weather Service San Juan PR 458 PM AST Wed Nov 29 2023


SYNOPSIS

Mainly fair weather conditions will prevail for the rest of the day into the night hours. Similar weather conditions will persists until Saturday morning, when an increase in moisture from the remnants of a frontal boundary will moves in, increasing the frequency of the showers, especially over the northern coastline of Puerto Rico and the local waters.

SHORT TERM
Today through Friday...

Minimum temperatures were once again in general between the low to mid 70s across the lower elevations, and from the low to mid 60s across the higher elevations. Little to no rainfall was detected over land areas through the early morning hours. Mostly sunny to partly cloudy skies are expected to prevail across the islands during today.

A mid-to upper-level ridge over the Caribbean basin will continue to promote fair weather conditions across the region through at least Thursday. Drier mid-level air, warm 500 mb temps, and overall stable conditions are expected to inhibit shower development across Puerto Rico and the U.S. Virgin Islands during the next few days. Shallow layer cloud development and light showers are expected at times through this period. By Friday, a wind surge is expected across the area as a strong low-level ridge is expected to develop over the western Atlantic, while an upper level trough and associated frontal boundary brings an increase in moisture content from the Atlantic waters. Therefore, isolated to scattered showers should increase on Friday across the area.

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

Little changes to the long term forecast. Current model suggest an increase in moisture, to normal precipitable water (PWAT) values, to start the weekend. According to current model guidance, the driest period would be on Sunday evening to early Monday morning, as a dry patch moves over the region, lowering PWAT values to below normal. A mid level ridge will move westward and weaken to start the period, strengthening again by the end of the period. At surface level, a high pressure will be established north of the islands over the western to central Atlantic, gradually moving eastward through the period, and being more confined to the tropical Atlantic. Most available moisture should remain below 800 mb. Slightly more humid air aloft is present Friday and Saturday, as a nearby polar trough and a lower level weak front approaches the region. For Sunday onwards, drier air is forecast aloft. East-northeast winds are forecast for the weekend, becoming more easterly to start the next workweek. As moisture increases the chance of passing showers across windward sectors of the islands will increase, as well as afternoon convection, fueled by local effects. For the weekend, afternoon convection should affect interior to western/southwestern Puerto Rico, under east-northeast winds.

AVIATION
Generally VFR through the period, with breezy easterly/northeasterly winds prevailing at all sites. There will be slight chance for VCSH/ISO SHRA across eastern PR and USVI overnight. Winds will become more light from 29/22Z to 30/14Z.

MARINE
A frontal boundary moving northeastward across the Western Atlantic and a high pressure ridge north of the region, will promote light to moderate easterly winds across the regional waters. By Thursday, a building surface high pressure will con and spread across the west and central Atlantic, promoting moderate to locally fresh winds and choppy seas. Marine conditions are forecast to deteriorate by the end of the work week due to the arrival of a northerly swell and increasing trade winds. There is a moderate risk of rip currents overnight into early Friday for the northern coastline of Puerto Rico, Culebra and Vieques, as well the U.S. Virgin Islands. L

SJU WATCHES/WARNINGS/ADVISORIES
PR...None.
VI...None.
AM...None.

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