Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
674 FXCA62 TJSJ 090903 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 503 AM AST Tue Dec 9 2025 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 449 AM AST Tue Dec 9 2025 * Marine and beach conditions will deteriorate by the second part of the workweek, expect choppy to rough seas and life- threatening rip currents. * Winds will increase late in the week, leading to breezy to windy conditions across coastal and elevated areas, lightweight outdoor items may be blown around in exposed locations. * For Puerto Rico, showers are expected to continue during the morning hours across the east/southeastern portions. Over west/northwest PR, afternoon showers are expected each day. * For the U.S. Virgin Islands, passing showers will continue throughout the morning, becoming frequent later tonight and early tomorrow. && .Short Term(Today through Thursday)... Issued at 449 AM AST Tue Dec 9 2025 Satellite imagery and Doppler radar early tonight showed an area of higher moisture and increased cloud cover associated with a weak surface perturbation drifting across the islands. This feature briefly enhanced shower activity over the U.S. Virgin Islands, Vieques, Culebra, and the southeastern coastal areas of Puerto Rico. However, rainfall accumulations were minimal. For today, the mid-level ridge will continue to influence the region, shifting slightly eastward as some troughiness approaches from the northwest. Model guidance indicates that 500 mb temperatures will be at their lowest of the short-term period. As a result, 700-500 mb lapse rates will steepen slightly, providing marginal instability. However, mid-level dryness will continue to limit vertical development, keeping most showers shallow. The weak trade wind perturbation will support variable cloudiness and passing morning showers over windward coastal sectors, followed by localized afternoon showers across the interior and western/northwestern Puerto Rico due to diurnal heating and sea breeze convergence. Wednesday remains slightly wetter. Model guidance indicates increasing moisture throughout the column, with precipitable water values nearing 2.0 inches and 700500 mb relative humidity rising to above-normal levels. This additional moisture, combined with gradually strengthening easterly to east-southeasterly winds and marginal instability, will promote more frequent showers. Afternoon convection over the interior and western portions of Puerto Rico will be deeper than in recent days, and a few isolated thunderstorms cannot be ruled out. Thursday will feature a pattern similar to today, with shallow moisture embedded in the trade wind flow supporting passing nighttime and early morning showers over windward areas, followed by isolated to scattered afternoon showers across the interior and west/northwest Puerto Rico. However, rainfall accumulations may be lower than today as breezy to locally windy conditions are expected, leading to quick-moving showers. && .Long Term(Friday through Tuesday)... Issued at 449 AM AST Tue Dec 9 2025 Mostly fair conditions are expected to persist this upcoming weekend, becoming variable early next week. As mentioned in the previous discussions, a surface high pressure over the Central Atlantic will strengthen, tightening the pressure gradient, with SE winds promoting breezy to locally windy conditions on Friday and Saturday. Additionally, a mid-level ridge lingering northeast of the CWA should serve as a blocking pattern, as shower activity will mostly be limited through at least Sunday. Nevertheless, troughiness in the mid to high levels may weaken the mid-level ridge, slightly cooling 500 mb temperatures (between -6 and -7 degrees Celsius), and bringing marginal instability. From the latest model guidance, PWAT values are expected to increase by early Monday, although model solutions show high variability as ensemble members show a spread between 1.2 - 1.6 inches. The most likely scenario is an increase in frequency of showers early Monday over the windward sections of the islands, with afternoon convection over western and northwestern PR, including the San Juan streamer. The latest model solutions also suggest that the proximity of a col region north of the region may weaken winds, promoting slow-moving showers. Taking into account possible marginal instability conditions, the flooding potential may increase during the afternoons, with mostly ponding of water over roadways and poorly drained areas, and a low chance of urban and small stream flooding. Although widespread lightning risk is not likely, short-lived isolated thunderstorms cannot be ruled out. As winds are likely to remain from the southeast, model guidance continues to suggest warmer-than-normal 925 mb temperatures, particularly during peak daytime hours. As mentioned in the previous discussion, the heat index in localized areas over the lower elevations of the islands may reach 100 degrees Fahrenheit, but no heat threat is expected during the period. && .AVIATION... (06Z TAFS) Issued at 449 AM AST Tue Dec 9 2025 Mainly VFR conds expected across all terminals. Brief -SHRA/VCSH will continue to move in from the E, mainly affecting USVI terminals (TIST/TISX) and occasionally TJSJ through 09/14z, with brief MVFR/IFR VIS/CIGs psbl. Sea-breeze influences aft 14Z may trigger SHRA/VCSH at TJBQ and interior PR. Winds light/vrb overnight, becoming ESE 1015 kt with ocnl higher gusts aft 14Z. && .MARINE... Issued at 449 AM AST Tue Dec 9 2025 A broad surface high pressure over the Central Atlantic will promote east to southeast gentle to moderate winds today through Wednesday. The high pressure will strengthen and tighten the pressure gradient and increase winds, allowing seas to build across the Atlantic waters and exposed passages. Additionally, a long-period northerly swell arriving early Thursday will further worsen conditions. Choppy to rough seas are expected, with Small Craft Advisories likely by the end of the workweek. A gradual improvement remains possible by the weekend as winds and swell ease. && .BEACH FORECAST... Issued at 449 AM AST Tue Dec 9 2025 The moderate risk of rip currents will continue over the north and east-facing beaches of Puerto Rico and the U.S. Virgin Islands through at least Wednesday. Beachgoers are encouraged to exercise caution as life-threatening rip currents are possible along the surf zone. A long-period northerly swell is expected to arrive early on Thursday, and spread across the local waters and passages. Combined with increasing winds, beach conditions are very likely to deteriorate and become dangerous mainly along north- facing beaches of the islands. Residents and visitors are urged to check the beach forecast before going out, and heed the advice of the flag warning system. As the swell ease and winds weaken, beach conditions should improve by the latter part of the weekend. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM/AVIATION...CVB LONG TERM/MARINE...MNG