Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
581 FXCA62 TJSJ 041650 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 1250 PM AST Thu Dec 4 2025 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 1215 PM AST Thu Dec 4 2025 * A weak surface trough will continue to increase cloudiness and shower activity over the islands through tonight. Urban and small stream flooding likely over southwestern PR this afternoon. Elsewhere, ponding of water on roads expected. * Fair weather conditions are expected from Friday into the upcoming workweek across all islands. * Slightly warmer daytime temperatures will persist over the islands, surpassing seasonal normals, especially in urban and coastal areas. * A moderate risk of rip currents will persist into the weekend across all eastern and northern beaches of PR and the USVI. && .Short Term(This evening through Saturday)... Issued at 1215 PM AST Thu Dec 4 2025 Sunny to partly cloudy skies prevailed across Puerto Rico and the U.S. Virgin Islands through the morning hours. Showers increased late in the morning over the eastern half of PR and over the USVI under the influence of a surface trough. As of 1230 PM, maximum temperatures were from the mid to upper 80s across the lower elevations of the islands, and in the upper 70s across the higher elevations of Puerto Rico. The wind was from the northeast between 10 and 15 mph with sea breeze variations and higher gusts across the southern coastal areas. For the rest of the afternoon hours, additional showers and isolated thunderstorms are expected to develop along portions of the Cordillera and south-southwest PR. Urban and small stream flooding is likely with this activity, particularly over southwestern PR. The bulk of moisture of the trough is well south of the region, however, another band of moisture is reaching the Leeward Islands and this will bring passing showers this evening across the USVI and across the eastern half of PR through tonight. For Friday and Saturday, a mid-to upper-level ridge building from the west will promote drier air intrusion, warmer mid-level temperatures and more stable conditions. At the surface, a weak high pressure will gradually build north of the area late in the period. This weather pattern will support overall fair weather conditions across the islands, with limited rainfall accumulations over land areas. However, locally induced afternoon showers cannot be ruled out over western PR each day, with minor flooding concerns. && .Long Term(Sunday through next Wednesday)... Issued at 340 AM AST Thu Dec 4 2025 The long-term forecast remains on track. A strong mid to upper- level ridge will be the main weather feature, mainly resulting in a stable weather pattern during the period. At 500 MB, temperatures in the -5 to -6 degree range and the 850 to 700 MB lapse rate, two standard deviations from the climatological values, will limit vertical development. Although very stable conditions will prevail, a strong surface high pressure over the Central Atlantic will drag patches of trapped moisture at 850 MB. According to the global model guidance, precipitable water values associated with the moisture patches will range from 1.4 to 1.6 inches, close to the climatological normals. Therefore, in the afternoon, brief passing showers are possible due to diurnal heating and local effects. On Sunday, surface winds will remain mostly from the east as the surface high pressure remains in the Central Atlantic. Veering winds are forecast from Monday onwards as the surface high pressure builds further into the Central and Eastern Atlantic. Since the surface winds will remain east-southeasterly and plenty of sunshine will be present due to the lack of instability, daytime temperatures will remain just slightly above seasonal levels across the islands. According to the global model guidance, 925 MB temperatures suggest warmer conditions from Monday onwards, with Tuesday the warmest day of the long term. && .AVIATION... (18Z TAFS) Issued at 1215 PM AST Thu Dec 4 2025 A weak surface trough should increase -SHRA across most terminals through at least tonight. However, iso TSRA expected to develop in and around TJPS and in the vcty of TJBQ this afternoon. Therefore, tempo MVFR conds are possible at these sites. The 04/12z TJSJ sounding indicated ENE winds up to 19 kt blo FL100. && .MARINE... Issued at 1215 PM AST Thu Dec 4 2025 Showers and isolated thunderstorms are expected today across portions of the Caribbean waters and coastal waters of the islands as a weak trough is moving over the region. An east to northeast 4 to 5 ft swell around 10 seconds and increasing trades will promote choppy seas across most offshore waters and local passages through the weekend. A building surface high pressure north of the area will maintain moderate to locally fresh trades (easterlies) through early next week. && .BEACH FORECAST... Issued at 1215 PM AST Thu Dec 4 2025 An east to northeasterly wind swell will promote a moderate risk of rip currents along the north and east facing beaches of Puerto Rico, including Vieques and Culebra, and across the U.S. Virgin Islands. These conditions will persist through the weekend. A moderate risk of rip currents means that life-threatening rip currents are possible and can quickly pull swimmers away from shore. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...DSR LONG TERM....LIS AVIATION...DSR BEACH/MARINE...DSR