Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
173 FXCA62 TJSJ 260804 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 404 AM AST Wed Jun 26 2024 .SYNOPSIS... The dense plume of Saharan Dust will continue to affect the local islands through Thursday. This plume will continue to promote hazy skies, lower visibilities and hot temperatures across the area. Expect warmer than normal temperatures each day, resulting in excessive heat warnings and heat advisories across Puerto Rico and the USVI. && .SHORT TERM...Today through Friday... Saharan dust and warmer than normal temperatures are expected to continue through at least Thursday across the U.S. Virgin Islands and Puerto Rico. An Excessive Heat Warning and a Heat Advisory are in effect for all coastal counties, please refer to the latest heat product NPWSJU for more information. Heat indices higher than 112 degrees Fahrenheit are expected. Hazy skies will continue today as the area remains under the influence of a strong Saharan Air Layer with moderate to high concentrations of Saharan dust. This drier air mass will limit shower activity in general, but diurnally induced streamers developing off the USVI and smaller islands are possible, in addition to isolated thunderstorms developing this afternoon over west/northwest PR. On Thursday and Friday, a gradual increase in moisture content is expected as an induced perturbation on the trade winds moves from the east. A 700-500MB ridge north of the region will promote northeasterly steering winds, while mainly easterly trades prevail at the surface due to the Azores High. This will cause showers and thunderstorms to develop over the interior and south/southwestern quadrant of Puerto Rico, while an advective pattern with passing showers persists across the USVI and the east/northeast sections of PR. && .LONG TERM...Saturday through Wednesday... The latest precipitable water guidance suggests values ranging around normal climatological levels across Puerto Rico and the U.S. Virgin Islands during the weekend. Nonetheless, as a surface high-pressure system positions across the Atlantic basin, we anticipate the introduction of tropical moisture into the islands through at least the upcoming workweek. This weather pattern will allow moisture to filter over the islands from time to time, and this, combined with the diurnal heating, will promote the development of afternoon showers and isolated thunderstorms, particularly across the western interior sections of Puerto Rico, as mostly easterly winds will dominate the forecast area. As mentioned in previous discussions, the tourists and citizens of Puerto Rico and the U.S. Virgin Islands will experience a slight change in weather conditions as drier air will filter across the region on Monday, reducing the chance of showers through Tuesday. Nevertheless, a typical seasonal weather pattern of passing showers and afternoon convection is expected. On Wednesday, expect a gradual increase in shower and possible thunderstorm activity across the forecast area, particularly over the Caribbean waters, as a tropical wave now being monitored by the National Hurricane Center moves south of us. However, we encourage people to stay updated with any changes in the forecast. && .AVIATION... (06Z TAFS) Mainly VFR conditions are expected to prevail across all terminals during the next 24 hours. HZ due to Saharan dust could drop VSBY around 6 miles. SHRA/TSRA is expected to develop btw 26/18z-22z in and around TJBQ, causing tempo MVFR conds. ESE winds expected at 12- 16 kt with stronger gusts and sea breeze variations aft 26/14z. && .MARINE... A surface high pressure over the central Atlantic will promote light to moderate east-southeasterly winds. Trade wind showers will move across the regional waters from time to time due to a tropical wave moving south over the Caribbean Waters. Hazy skies are expected through Thursday due to Saharan dust. && .BEACH FORECAST... There is a moderate risk of rip currents across southern PR and St. Croix. A low risk is forecast elsewhere. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Excessive Heat Warning from 10 AM this morning to 6 PM AST this evening for PRZ001-003-005-007-008-010>012. Heat Advisory from 10 AM this morning to 6 PM AST this evening for PRZ002-013. VI...Excessive Heat Warning from 10 AM this morning to 6 PM AST this evening for VIZ002. Heat Advisory from 10 AM this morning to 6 PM AST this evening for VIZ001. AM...None. && $$ SHORT TERM/AVIATION...DS LONG TERM/MARINE/BEACH FORECAST...MMC