Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
404 FXCA62 TJSJ 240918 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 518 AM AST Tue Sep 24 2024 .SYNOPSIS...Warm-to-hot conditions will continue today. Winds will increase a little Wednesday through Friday when a tropical wave will move through--mostly south of the area. Warm and moist conditions will continue through the weekend followed by somewhat drier conditions in the first few days of next week. && .SHORT TERM...Today through Thursday... Tonight, mostly fair weather conditions prevailed inland across Puerto Rico and the U.S. Virgin Islands. However, some lightning activity lit the sky, particularly along the northern, western, and southern coastal areas of Puerto Rico and the U.S. Virgin Islands, as some showers and isolated to scattered thunderstorms developed over the Atlantic and Caribbean waters and the waters between the U.S. Virgin Islands and the Mona Passage. The overnight temperatures remained in the lower 70s in the higher terrain and in the upper 70s to lower 80s in the urban/coastal areas. Like previous days, the winds were relatively light and variable across the islands. The short-term forecast remains unchanged. According to the latest model guidance, the upper-level trough will continue to move from the western Atlantic and will position to the north of our forecast area, enhancing the upward vertical motion and better moisture content today. Therefore, showers and thunderstorms will increase in coverage once again, particularly this afternoon. Weak steering winds will also lead to higher rainfall accumulations over the same areas, increasing the potential for flooding and mudslides in steep terrain, mainly along the Cordillera Central. On Wednesday, winds are expected to become slightly stronger, around 10 to 15 knots, as the deep-level trough will be out of the area by then. As mentioned in previous discussions, the U.S. Virgin Islands should experience a similar weather pattern over the next few days, with little to no rain. However, showers and thunderstorm development are forecast over the waters near the USVI. Temperatures will be in the upper 70s to lower 80s over the higher terrain, and upper 80s to lower 90s will persist across the lower elevations of the islands during the morning and early afternoon hours. Therefore, excessive heat conditions can be anticipated throughout the short-term period. Advisories and warnings for heat have been issued again today. && .LONG TERM...Friday through Tuesday... A band of moisture will move through early Friday morning followed by a tropical wave--most of which will pass south of the forecast area Friday night. Nevertheless some increase in rainfall is expected, despite the fact that 500 mb temperatures will be warmer than those of today and Wednesday. Precipitable water will be found mostly between 1.95 and 2.05 inches even though the good moisture is mostly supplied by the lower layers. While strong low pressure systems will be found to the distant northwest, north northeast and east, the flow across the local area on Thursday will be easterly at 12 to 18 knots. The tropical wave will pass through on Friday with oscillations in the flow over the weekend. Finally on Monday and Tuesday flow at the surface becomes light southerly. High pressure will again nose in from the east northeast and conditions will dry out a little. Most days during the long term period will still see afternoon convection over the western and interior portions of Puerto Rico. On Monday and Tuesday the showers and thunderstorms could also draw near to the Greater San Juan and Bayamon Metropolitan areas. At mid levels high pressure dominates the synoptic pattern while in upper levels high pressure will remain to the northwest although still quite influential in maintaining the dryness of the mid to upper layers. && .AVIATION... (06Z TAFs) Mostly VFR conditions at all TAF sites. Clds and SHRA are expected to dvlp across the interior sections of PR aft 24/17Z, followed by SHRA/TSRA with mtn obscurations and MVFR conds over the interior through 24/22Z. TJSJ and TJBQ will experience brief MVFR conds, particularly after 18Z. Winds less than 11 kt with a few higher gusts along the coasts and near TSRA till 24/22Z. TSRA will still be found offshore aft 24/22Z. && .MARINE...A slight north to northeast swell will move into the area on Wednesday and strengthen on Friday. Winds will increase Wednesday through Friday, but gradually subside again on Monday and Tuesday. Small craft advisories are not expected during the next 7 to 10 days, but small craft will need to exercise caution in some areas. Conditions will improve Monday and Tuesday of next week. && .BEACH FORECAST...We will see one more day where all beaches will have a low risk of rip currents and then north and northeast facing beaches will begin to have a moderate risk of rip currents. Conditions improve again Monday night and Tuesday of next week. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Heat Advisory from 11 AM this morning to 5 PM AST this afternoon for PRZ001>003-013. Excessive Heat Warning from 11 AM this morning to 5 PM AST this afternoon for PRZ005-007-008-010-011. VI...Excessive Heat Warning from 11 AM this morning to 5 PM AST this afternoon for VIZ002. AM...None. && $$ SHORT TERM/AVIATION...MMC LONG TERM/MARINE....WS