Leeward Islands Offshore Forecast
| Today...E To Se Winds 10 To 15 Kt. Seas 3 To 5 Ft. |
| Tonight...E To Se Winds 10 To 15 Kt. Seas 3 To 5 Ft. |
| Wed...E To Se Winds 10 To 15 Kt. Seas 3 To 5 Ft. |
| Wed Night...In The Caribbean, E Winds 10 Kt. In The Atlc, E To Se Winds 10 Kt In The Evening, Becoming Variable Less Than 5 Kt. Seas 3 To 5 Ft. |
| Thu...In The Caribbean, E Winds 10 Kt In The Morning, Becoming Variable Less Than 5 Kt. In The Atlc, Variable Winds Less Than 5 Kt. Seas 3 Ft Or Less In The Caribbean, And 3 To 5 Ft In The Atlc. |
| Thu Night...Variable Winds Less Than 5 Kt. Seas 3 Ft Or Less In The Caribbean, And 4 To 6 Ft In The Atlc. |
| Fri...In The Caribbean, Ne To E Winds 10 Kt In The Morning, Becoming Variable Less Than 5 Kt. Seas 3 Ft Or Less, Building To 3 To 5 Ft In The Afternoon. In The Atlc, Variable Winds Less Than 5 Kt. Seas 6 To 9 Ft. |
| Fri Night...In The Caribbean, E Winds 10 Kt. In The Atlc, Ne To E Winds 10 Kt In The Evening, Becoming Variable Less Than 5 Kt. Seas 4 To 6 Ft In The Caribbean, And 6 To 9 Ft In The Atlc. |
| Sat...In The Caribbean, E To Se Winds 10 Kt. In The Atlc, E Winds 10 Kt In The Morning, Becoming Variable Less Than 5 Kt. Seas 4 To 6 Ft In The Caribbean, And 6 To 9 Ft In The Atlc. |
| Sat Night...E Winds 10 Kt. Seas 4 To 6 Ft In The Caribbean, And 6 To 9 Ft In The Atlc. |
| Area Forecast Discussion National Weather Service San Juan PR 209pm AST Tuesday September 30 2025 .KEY MESSAGES... * Isolated to scattered showers with isolated thunderstorms are expected across the northwest quadrant of Puerto Rico this afternoon. * Across the U.S. Virgin Islands, a showery pattern will tonight into Wednesday morning. * A Heat Advisory remains in effect for all urban and coastal areas of Puerto Rico and the U.S. Virgin Islands until 5pm AST. Stay hydrated and avoid prolonged sun exposure. On Wednesday, conditions will support an even warmer day, with the potential for additional Extreme Heat Warnings or Heat Advisories. * A large, long-period northerly swell arriving by late Thursday night will promote hazardous marine and beach conditions across the islands, persisting through at least Sunday or early next week. .SHORT TERM...Tonight through Thursday... Current satellite derived precipitable water (PWAT) values show that a band of moisture, with values ranging from 1.9 to 2 inches, trailing distant Humberto already over the Mona Passage and moving westward. Drier air continues to filter into our area with values ranging to around 1.6 to 1.8 inches over the region, with the highest values observed over NW PR, where later convective activity continues to be forecast. This drier air mass and overall unfavorable conditions have served to limit today's afternoon convection, however increasing 700 to 500 mb lapse rates and decreasing 500 mb temperates are still forecast during the rest of the period. This is due to a series of short-wave troughs along a ridge north of the region. Elevated, to possibly significant tomorrow, heat risks will continue across urban and coastal elevations of the islands. Heat Advisories will likely be issued each day with an Extreme Heat Warning possible tomorrow, in part due to weak southerly flow tomorrow. A more northern component can bring some light relief Thursday. 925 mb temperatures are forecast at 2 standard deviations above normal while reaching 1 SD above normal on Thursday. Available moisture reaching the region should remain with below to normal PWAT (Precipitable Water) values, reaching normal values with isolated patches of higher moisture reaching the islands. Afternoon showers and t-storms are expected to develop along the interior each afternoon, steered by the weak above mentioned flow. Diurnal heating, lighter flow will also help this convective activity develop, and possibly linger longer. Passing showers continue to be forecast across windward sectors each day. Lines of showers can also develop downwind of the local islands during each afternoon. Long Term Friday through Tuesday... /FROMIssued at 507am AST Tuesday September 30 2025/ Variable conditions are expected through the long-term forecast. Winds will remain light and variable due to a col region developing over the area, slightly increasing by Sunday, then becoming lighter by the start of next workweek. As mentioned in the previous drier air mass is expected to filter into the region due to the influence of a mid- level ridge that is expected to linger northeast of the region. However, the latest model guidance suggests that a mid-to- upper trough may move south of the CWA (County Warning Area) by Friday and Saturday. The presence of this feature is reflected in the projected 500 mb temperatures (between -6.5 and -7.5 degrees Celsius), near below climatological normals, enhancing the deep convection activity. As the deterministic guidance of the GFS (Global Forecast System) and ECMWF (European Centre for Medium-Range Weather Forecasts) continues to suggest low to seasonal PWAT (Precipitable Water) values (1.6 - 1.8 inches), expect seasonal weather conditions during the upcoming weekend, with isolated showers moving over the local waters into windward sectors and afternoon convection. Taking into consideration the wind speed, there’s a high chance that any shower developing over the area will stay stationary, meaning that the flood potential will be more localized, particularly over the mountain ranges of Puerto Rico. By early next week, a gradual increase in moisture content and favorables conditions for deep convection are likely due to a series of upper level troughs approaching the CWA. From the latest model guidance, PWAT (Precipitable Water) values should increase close to near above normal values (1.8- 2.0 inches, low chance of reaching 2.2 inches). This could increase the frequency of showers and thunderstorms moving across the local islands on Monday and Tuesday, elevating flood potential. Given the expected conditions, the flooding threat will remain from limited to elevated for the rest of the forecast period. The tendency of warmer conditions across the islands is expected to continue due to above-normal temperatures, available moisture, and light winds. Hence, the heat threat will remain limited to elevated for the urban and coastal areas of Puerto Rico and the U.S. Virgin Islands. Marine Moderate southeasterly to easterly winds will continue tonight, becoming gentle by Wednesday night and Thursday. A large, long- period northerly swell generated by distant hurricanes Humberto and Imelda will likely promote hazardous marine conditions for small craft across the Atlantic waters and local Caribbean passages from late Thursday night through at least Sunday or early next week. Mariners are urged to monitor the forecast over the coming days, and those operating smaller vessels should consider avoiding navigation during this upcoming period. Beach Forecast Tonight, the risk of rip currents is expected to remain moderate for the north-facing beaches of Puerto Rico, including Culebra, as well as St. Thomas and St. John in the U.S. Virgin Islands. Beachgoers are urged to exercise caution at all times, as a moderate risk means life-threatening rip currents are possible within the surf zone. A low risk remains in place elsewhere. Conditions are expected to improve by tomorrow, Wednesday, however, a large, long-period northerly swell anticipated to arrive by late Thursday night will promote life-threatening rip currents through at least early next week. Additionally, there is potential for large breaking waves to trigger High Surf conditions. Beachgoers are encouraged to continue monitoring the forecast and heed the advice of the flag warning system over the coming days. Additional beach hazards this afternoon and in the days ahead include afternoon thunderstorms, especially along northwestern beaches and heat risk, typically from 10am to 5 PM. Stay well hydrated, and remember that if you hear thunder, you should seek shelter in a safe indoor location. .SJU WATCHES/WARNINGS/ADVISORIES... PR... Heat Advisory until 5pm AST this afternoon for PRZ001>005-007- 008-010>013. VI... Heat Advisory until 5pm AST this afternoon for VIZ001-002. AM...None. |