198 FXCA62 TJSJ 202122 RRA AFDSJU Area Forecast Discussion...DELAYED National Weather Service San Juan PR 522 PM AST Wed Nov 20 2024 .SYNOPSIS... Stable weather conditions will persist for the next few days. However, weather conditions will deteriorate this weekend as a polar trough and a surge of tropical moisture settles over the northeastern Caribbean. Hazardous marine conditions will persist tonight and return during the weekend. && .SHORT TERM...Today through Friday... Mostly sunny to partly cloudy skies prevailed across the islands today. Scattered showers were noted mainly across the northeastern sections of Puerto Rico throughout the day. The Doppler radar estimated around three tenths of an inch over Fajardo. High temperatures were in the mid to upper 80s across most urban areas of the lower elevations, and once again in the low 90s in Ponce and Guanica. A high of 88F was reported at the St. Thomas and St. Croix airports. The wind prevailed from the northeast between 8 and 12 mph with higher gusts and sea breeze variations along the southern coast of PR. The highest wind gust reported today was 26 mph at the King Airport in St. Thomas. A polar trough will exit the eastern coast of the U.S. by Friday, while a weak surface high pressure north of the area moves further eastward into the central Atlantic. This will cause winds to gradually veer and become more easterly by late tonight, southeasterly by Thursday afternoon, and then southerly by Friday. A surface front will also move across the western Atlantic and a pre- frontal trough is expected to develop over the northeastern Caribbean, increasing moisture across the local area by the end of the workweek and into the weekend. Therefore, shower activity will increase in general over the USVI by Thursday and across the islands on Friday. A shift in steering winds from the east to southeast will favor shower development in the afternoon hours over portions of the interior and north/northwest Puerto Rico. High temperatures will be in the the mid to upper 80s across most coastal areas of the islands, except in southern PR where it can reach the low 90s once again on Thursday and Friday, while the minimum temperatures could drop into the low 60s across the higher elevations and mountain valleys. && .LONG TERM...Saturday through Wednesday... .PREV DISCUSSION... /issued 540 AM AST Wed Nov 20 2024/ High pressure at upper levels dominates the long period despite the passage of an upper level trough saturday evening well to the north of the area. The associated southwesterly jet stream will likely never get past Cuba. At mid levels high pressure becomes entrenched about 1000 miles east northeast of San Juan, Puerto Rico and moves very little. As the flow around this high is from the south modest moisture will be brought up out of the Caribbean during the period. Peak moisture will be seen late Sunday night and Monday morning. At the surface high pressure northeast of the area--much where the mid level high is also--keeps flow southerly. A weak wave passing to the west over the Caribbean begins to amplify south of Jamaica and flow turns southeasterly for the remainder of the period. While this does bring in some moisture, flow is never particularly moist at any one level but precipitable water values remain above two inches except for a 24 hour period from early Tuesday to early Wednesday when air from the mid Atlantic is brought back in around the high pressure east northeast of the area. While the low pressure expected to form over the Central Caribbean will not directly affect Puerto Rico or the U.S. Virgin Islands, periods of showers will keep the area wet. At this time this does not appear to generate expectations for anything more than ponding of roads and some stream rises. && .AVIATION... (18Z TAFS) Mainly VFR conditions are expected to prevail across all terminals during the next 24 hours. However, diurnally induced SHRA may cause periods of -RA/VCSH in and around the USVI/PR terminals btw 21/16z- 22z. NE winds up to 10 knots blo FL040 will continue to prevail across most terminals with land/sea breeze variations. && .MARINE... Gentle to moderate northerly winds will prevail through late tonight, when easterly winds return. Pulses of the northerly swell will continue to arrive tonight, but conditions are likely to remain below small craft advisory criteria. Another small long-period northerly swell is expected for the weekend. && .BEACH FORECAST... Buoy 41043, about 170 NM NE of San Juan indicated a 7 ft swell at 11-13 seconds and should persist through late tonight. The local San Juan now indicates seas at 6 ft at 12-14 seconds. Therefore, a High Surf Advisory was added to the northern coastal area of Puerto Rico while the High Rip Current Risk was extended through at least 6 PM Thursday. Please refer to CFWSJU. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through Thursday afternoon for PRZ001-002- 005-008-010-012. High Surf Advisory until 6 PM AST Thursday for PRZ001-002-005- 008. VI...High Rip Current Risk through Thursday afternoon for VIZ001. AM...None. && $$ SHORT TERM...DSR/CVB MARINE/BEACH...CVB LONG TERM...PREV AVIATION..ICP/DSR
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