Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
905 FXCA62 TJSJ 051819 AFDSJU Area Forecast Discussion...RESENT National Weather Service San Juan PR 219 PM AST Sat Sep 5 2026 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 158 PM AST Sat Sep 5 2026 * Higher humidity and hot conditions will increase the heat threat across the islands from Sunday into the workweek. However, on Sunday, upper cloudiness might reduce the sunshine exposure, limiting the period of the threat. * A wet and unsettled weather pattern is expected as a tropical wave, in combination with an upper-level low over the western Atlantic, results in showers and thunderstorms across the islands from Sunday into Monday. * A low risk of rip currents will remain in place for all coastal areas at least through Monday, increasing to moderate for the northern coast of Puerto Rico and the U.S. Virgin Islands. * By midweek, models suggest an increase in Saharan dust particles across the region, resulting in hazier skies and limiting shower development. && .Short Term(This evening through Monday)... Issued at 158 PM AST Sat Sep 5 2026 Cloudy skies remained across the islands, with some passing showers across eastern and southeastern sections of Puerto Rico. The shower activity observed by the Doppler radar was quite minimal, and rainfall accumulations were less than half an inch. As of 12 PM, some limited showers were spotted across the interior sections and areas of San Juan. Warm conditions were observed across the islands with heat indices between 100 and 112 degrees. Across the interior sections, heat indices fluctuated between 88 and 105 degrees. Winds were from the southeast at 15 mph or less, with wind variation along the coastal areas. For the rest of the short-term period, a broad surface high pressure extending across the central Atlantic will continue to dominate the local wind pattern, promoting southeasterly winds across Puerto Rico and the U.S. Virgin Islands. Meanwhile, a tropical wave moving across the eastern Caribbean will continue to increase the moisture field through the rest of today and into Sunday. This increase in tropical moisture, combined with local and diurnal effects, will favor increased shower activity across the islands. Aloft, an upper- level low near 250 mb will gradually become established over the forecast area, providing additional instability and resulting in plenty of upper-level cloudiness. Therefore, weather conditions are expected to remain unsettled and variable through Sunday, with periods of showers affecting mainly eastern and southeastern Puerto Rico and the U.S. Virgin Islands during the overnight and morning hours, followed by afternoon convection across portions of interior and western Puerto Rico and also the El Yunque area moving into the San Juan metro area. By Monday, the broad surface high pressure will remain over the central Atlantic, maintaining a generally southeasterly wind flow across the region. The pressure gradient is expected to strengthen slightly, resulting in moderate southeasterly winds. At the same time, abundant tropical moisture will remain across the region, with precipitable water values increasing to around 2.20 inches, which is well above normal for this time of the year. Despite the abundant moisture, the evolution of the upper-level low and periods of upper- level cloudiness will continue to influence the coverage and intensity of the convection. Nevertheless, the combination of deep tropical moisture, southeasterly flow, and local effects should support passing showers across the U.S. Virgin Islands and the windward portions of Puerto Rico during the morning hours, followed by another round of afternoon showers and thunderstorms, mainly across interior and western Puerto Rico. Given the high moisture content, any persistent or stronger shower activity could produce locally heavy rainfall and areas of ponding of water, with localized flooding possible in the low-lying areas. && .Long Term(Tuesday through next Friday)... Issued at 433 AM AST Sat Sep 5 2026 Recent model guidance has trended drier, suggesting limited prospects for meaningful rainfall relief from the ongoing drought and water-supply concerns. Ridging north to northwest of the region should promote generally dry and hot conditions Tuesday. A tropical wave will then approach as the ridge retreats and a trough develops east-northeast of the Caribbean, providing the best opportunity for increased moisture and convection Wednesday into early Thursday. However, uncertainty remains regarding the timing and depth of the moisture. A more extensive dry-air mass should follow the wave and persist through the weekend. Breezy to locally windy east- southeasterly conditions are also expected as high pressure strengthens across the North Atlantic. Extreme heat will likely remain the primary hazard, particularly Tuesday. Stronger winds, increased cloud cover, and showers may result in slightly lower temperatures Wednesday and Thursday. Although below-normal moisture may limit rainfall coverage and intensity, locally heavy rainfall could produce localized flooding Wednesday into Thursday, while thunderstorms will pose a lightning risk. Nevertheless, widespread or substantial rainfall is not anticipated. && .AVIATION... (18Z TAFS) Issued at 158 PM AST Sat Sep 5 2026 Mainly VFR conditions are expected to prevail across all terminals through the fcst period. However, locally induced SHRA/TSRA may result in tempo MVFR conditions at TJSJ/TJBQ thru 05/21z. Elsewhere, mostly VCSH/VCTS expected. ESE winds will continue through early this evening between 8-12 kt with sea breeze variations and stronger gusts at times. Light and variable winds are expected overnight. && .MARINE... Issued at 158 PM AST Sat Sep 5 2026 Light to moderate southeast winds will prevail through at least Monday. Winds will strengthen and become moderate to fresh from Tuesday onward as a surface high pressure builds across the central Atlantic, resulting in choppy seas up to 6 feet and east winds up to 20 knots. Moisture ahead of a tropical wave will continue to bring scattered showers and isolated thunderstorms across the regional waters today, and linger through Monday. && .BEACH FORECAST... Issued at 158 PM AST Sat Sep 5 2026 A low risk of rip currents will continue through late Monday. Although the risk remains low across all beaches of the islands, beachgoers must pay attention as life-threatening rip currents often occur near jetties, piers, reef, and groins. By Tuesday, the risk will increase to moderate, as winds increase and seas gradually build to around 4 or 5 feet across the coastal waters of the islands. The moderate risk is expected mainly across the northern and eastern beaches of the islands on Tuesday, spreading across most beaches during the second part of the workweek. Aside from rip currents, showers and isolated thunderstorm are expected each afternoon, moving near coastal areas of the islands, bringing gusty winds and lightning. Beachgoers must seek shelter whenever they hear thunder. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>013. VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002. AM...None. && $$ KEY MESSAGES/SHORT TERM...LIS LONG TERM...ICP BEACH/MARINE/AVIATION...DSR