AFDSJU Area Forecast Discussion...CORRECTED National Weather Service San Juan PR 406 AM AST Tue Nov 18 2025 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 348 AM AST Tue Nov 18 2025 * Life-threatening rip currents are expected along the north- facing beaches in Puerto Rico, Culebra, and the eastern half of St. Croix through Wednesday afternoon. * Showers and isolated thunderstorms due a surface trough will increase the flooding and lightning risk today, particularly over western and northeastern Puerto Rico. * Passing showers will bring periods of moderate to locally heavy rain across the US Virgin Islands throughout the day. && .Short Term(Today through Thursday)... Issued at 348 AM AST Tue Nov 18 2025 Afternoon convection linger into the early evening hours across Arecibo, leaving rainfall accumulations of just over one inch. Additionally, the frequency of showers increased along the east, with nearly half an inch collected. Later in the overnight hours, showers also moved across the Virgin Islands. The heaviest activity was observed over eastern St. Croix, and also in St. John. Elsewhere, skies were mostly clear. Temperatures dropped into the low 60s or even a tad cooler in the mountains of Puerto Rico, with lows in the low and mid 70s in the coastal areas of the U.S. Caribbean territories. A surface trough moving across the region today will bring increasing moisture to the islands, with a moderate easterly breeze at the surface and southeast winds higher up steering showers and storms toward the west and west-northwest. Despite a weakening mid- level ridge, temperatures aloft will continue to cool ahead of the approaching mid- to upper-level trough, marking the onset of an unstable period beginning this afternoon. This setup will make today the wettest day of the period, with showers and isolated to locally scattered thunderstorms clustering across the central and western interior of Puerto Rico, with the strongest activity expected over the western hills. Additional pockets of heavy rain may also develop downwind of Sierra de Luquillo and the local islands, affecting parts of the San Juan metro area. Heavy downpours could cause localized flooding, with minor flooding or ponding of water possible in low-lying or poorly drained areas. Temperatures will remain near normal, with a few urban locations briefly reaching around 90F. Hazard Summary for Today: Expect a low to locally moderate flooding risk from heavy downpours and isolated to locally scattered lightning strike risk with thunderstorms. The mid-to upper-level trough will continue to move in tonight, keeping conditions unstable as colder mid-level temperatures persist. Once the trough axis moves through on Thursday morning, warming aloft and very dry air will quickly stabilize the atmosphere. At the surface, high pressure moving into the western Atlantic will strengthen local winds and shift them to the northeast tonight into Wednesday, producing a fresh breeze. On Thursday, a weak surface trough east of the Leeward Islands will help maintain the north-to-northeast flow, although at more moderate intensities. This pattern will bring in some moisture early on but will also push the existing moisture plume southward, allowing much drier and slightly cooler air to settle in later in the period. Moisture will be the main factor influencing rainfall, with levels rising slightly above normal tonight, returning to typical values Wednesday morning, and then steadily falling to well below normal by late Thursday. Overall, showers and thunderstorms will be more limited on Wednesday, with only a few brief storms possible, and by Thursday the weather will become mostly stable with little to no thunder expected. Despite the drying trend, a passing trade wind showers may still occur overnight, even during the driest periods, due to the steady northeast flow. Cooler temperatures near the surface will continue and may bring the first hint of a friito navideno feel later in the week. Hazard Summary for Tonight through Thursday: A limited flooding and lightning risk from locally heavy downpours produced by a few thunderstorms on tonight into Wednesday. && .Long Term(Friday through Tuesday)... Issued at 348 AM AST Tue Nov 18 2025 The long-term forecast remains on track, with mostly fair conditions for the upcoming weekend, becoming variable early next week. A surface high pressure is still expected to build over the Western Atlantic by Friday, promoting northeasterly winds through most of the period. As a drier air mass should filter into the region, the latest deterministic guidance from the GFS and ECMWF continues to suggest PWAT values mostly below climatological normal (1.2 - 1.4 inches), with a few members opting for more seasonal values (1.4 - 1.6 inches). A mid-level ridge should also establish, warming 500 mb temperatures (around -5.5 degrees Celsius), and promoting stability aloft and limiting deep convection activity. Additionally, the Galvez-Davison Index (GDI) suggests a low potential of thunderstorm development across the CWA. As mentioned in the previous discussion, the most likely scenario would be passing showers over windward sections in the late night and morning, with limited afternoon convection over the mountain ranges and southwestern portions of Puerto Rico. Although rainfall accumulations should not present a flooding threat, expect ponding of water over roadways, urban, and poorly drained areas. On Monday and Tuesday, PWAT values are expected to increase to more seasonal levels due to patches of moisture moving across the CWA, resulting in an increased frequency of showers. Nevertheless, no significant flooding or lightning risk is expected across the region. Once again, cooler temperatures are likely across the CWA during the forecast period, as the latest guidance keeps suggesting a fall in 925 mb temperatures, well below normal. Under a northeast wind flow, the heat threat will remain low throughout the long-term period. && .AVIATION... (06Z TAFS) Issued at 348 AM AST Tue Nov 18 2025 SHRA and iso TSRA are occurring near TJSJ and USVI terminals and will continue at times thru the prd. Aftn convection will expand toward TJBQ and TJPS, and all sites may experience brief MVFR due to mtn obsc and reduced VIS. SHRA will decrease aft 18/22Z but may linger near TJSJ and USVI terminals overnight. Winds will remain LGT/CALM and VRB early, increase to 812 kt btwn 18/13Z18/22Z, then return to LGT/VRB overnight. && .MARINE... Issued at 348 AM AST Tue Nov 18 2025 Winds from the east will increase and become moderate today, shifting from the northeast by Wednesday night. The approach of a surface trough will bring showers and isolated thunderstorms across the local water and passages, likely to generate localized hazardous marine conditions for small craft. Pulses of a north northeasterly swell will continue to spread across the Atlantic waters and local passages through Wednesday. && .BEACH FORECAST... Issued at 348 AM AST Tue Nov 18 2025 No changes were introduced to the beach forecast. Pulses of the northerly-northeasterly swell will continue to spread across the Atlantic waters and passages, promoting hazardous beach conditions. Hence, the high risk of rip currents remains for the northern and eastern beaches of Puerto Rico, including Culebra, and St. Croix in the U.S. Virgin Islands through Wednesday evening. Visitors and residents are encouraged to check the beach forecast before going, heed the advice of the flag warning system, and always swim near a lifeguard. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through Wednesday afternoon for PRZ001-002- 005-008-012. VI...High Rip Current Risk through Wednesday afternoon for VIZ002. AM...None. && $$