Leeward Islands Offshore Forecast
| Today...E To Se Winds 10 To 15 Kt. Seas 3 To 5 Ft. |
| Tonight...E Winds 10 To 15 Kt. Seas 2 To 4 Ft. |
| Thu...E To Se Winds 10 To 15 Kt. Seas 3 To 5 Ft. |
| Thu Night...E Winds 10 To 15 Kt. Seas 3 To 5 Ft. |
| Fri...E Winds 10 To 15 Kt. Seas 3 To 5 Ft. |
| Fri Night...E Winds 10 To 15 Kt. Seas 3 To 5 Ft. |
| Sat...E Winds 10 To 15 Kt. Seas 3 To 5 Ft. |
| Sat Night...E Winds 10 To 15 Kt. Seas 3 To 5 Ft. |
| Sun...E Winds 10 To 15 Kt. Seas 4 To 6 Ft. |
| Sun Night...E Winds 10 To 15 Kt. Seas 4 To 6 Ft In Ne To E Swell. |
| Area Forecast Discussion ...CORRECTED National Weather Service San Juan PR 448am AST Wednesday September 23 2026 .Short Term(Today through Friday)... Issued at 100am AST Wednesday September 23 2026 Overnight, conditions remain relatively calm with pockets of showers moving across the waters. Temperature remained in the upper 70s to low 80s along the urban and coastal areas of the islands, while across the interior and rural areas they dropped into the upper 60s to low 70s. During the morning hours, expect passing showers mainly over local waters and occasionally reaching eastern portions and the U.S. Virgin islands as precipitable water (PWAT) will remain within seasonal levels. Slightly drier air in the mid-to-high-levels should limit significant deep convection. However, nearby troughs, local effects and low-level moisture should still support brief convective periods by the afternoon hours. That being said, with the gentle to moderate winds from an east-southeasterly flow, expect the shower and thunderstorm activity to develop mainly over interior to northwestern portions of Puerto Rico. On Thursday, a couple of mid-to-upper-level lows approaching from the northeast will influence 500-mb temperatures to drop to sub- seasonal levels and enhance instability in the upper levels, which could result in deeper afternoon convection. In addition, moisture associated to a tropical wave will reach the islands by Thursday, increasing the potential for deeper convection. This scenario, combined with local effects and prevailing gentle to moderate winds from the ESE could allow shower and thunderstorm development primarily over interior to northwestern portions, while isolated activity is possible over eastern Puerto Rico, Vieques and Culebra. Following the tropical wave, slightly drier air with low concentrations of Saharan Dust will filter into the CWA (County Warning Area) on Friday, dropping PWAT (Precipitable Water) values to near normal fro this time of the year. Therefore, less showers and thunderstorms are expected, but still possible due to local effects and sufficient moisture levels in the low-levels to support isolated convection. An elevated heat risk is likely on Friday due to less cloud cover and shower activity expected, while it remains limited on Wednesday and Thursday. Overall, the primary weather hazards will include localized heavy rainfall, and isolated thunderstorms, which could be accompanied by frequent lightning and strong gusts, particularly on Thursday. An elevated risk of excessive rainfall will remain today, mostly over interior and northwestern Puerto Rico as saturated soils and elevated streamflows persist over that region. Any additional rainfall this afternoon will result in excessive runoff that could increase the flood threat in localized areas. The frequency of showers by tonight could increase across windward coastal areas of the forecast area as the leading edge of a tropical wave starts to move over the region. Elevated flooding threat will remain on Thursday as conditions become more favorable for stronger convection. Consequently, mainly today and Thursday, shower activity may lead to water ponding on roadways, urban and small stream flooding, and even isolated flash floods with periods of heavy rainfall, alongside a continued risk of landslides where terrain is already saturated from recent rainfall. .Long Term(Saturday through Wednesday)... Issued at 100am AST Wednesday September 23 2026 A couple of multi-level lows continue to be the main synoptic features over the region. An upper-level low will shift to the southwest of Puerto Rico and coupled with local effects will continue to drive instability that favors the development of showers and thunderstorms across the CWA. With the exception of Saturday, when model guidance suggests that a drier air mass from low to upper levels (700-250 hPa) accompanied with low levels of Saharan Dust will lead to amenable weather conditions. Precipitable water (PWAT) values are expected to be variable with lower values expected Saturday into Sunday, becoming seasonal on Monday and returning to a drier pattern Tuesday into Wednesday. A key feature for the weekend will be drier low-to-upper levels (700-250 mb). Thus, any activity that develops will heavily rely on the instability provided by the low as well as mechanical lifting mechanisms driven by local effects. A more humid vertical profile is expected on Monday making the day more favorable for convective activity. The mid-tropospheric temperatures will be well below the normal ranges for the season, thus this may favor the development of deep convective cells into early next week. Breezy conditions are expected to prevail on Tuesday into Wednesday, along with the ESE windflow set by the low- level low pressure system in the central to western Atlantic and a surface high over the central Atlantic surrounding the remnants of Fay. This ESE flow may favor the development of streamers off the US Virgin Islands, Vieques, Culebra, and El Yunque rainforest and convective activity from interior to west and northwest PR. One of the main risks for the long-term period remains associated to the extreme heat. Low-level (925 mb) temperatures are expected to be 2 standard deviations above normal levels, this accompanied with humid low-levels and calmer wind conditions will lead to an elevated extreme heat risk into early next week. Thus, we recommend individuals limit outdoor activities and remain well hydrated. Marine Issued at 100am AST Wednesday September 23 2026 A surface high pressure building across the north-central Atlantic will maintain light to moderate east to southeast winds through the end of the week. A small, long-period northeasterly swell will gradually arrive late today, increasing seas to 3 to 4 feet across the Atlantic and Caribbean waters, including the local passages. Additionally, expect afternoon thunderstorms to develop over the Atlantic and western coastal waters of Puerto Rico along with locally strong gusty winds, torrential rainfall, frequent lightning, and reduced visibility through the early evening hours each day. Small craft operators should use additional caution near thunderstorms, where conditions can deteriorate quickly. Mariners should monitor the latest forecasts and weather conditions before departure and while underway, and be prepared to adjust plans if thunderstorms approach. Beach Forecast Issued at 100am AST Wednesday September 23 2026 A low risk of rip currents is expected across most beaches of Puerto Rico and the U.S. Virgin Islands through this afternoon, as a small northeasterly swell gradually reaches the islands and increase the rip current risk to moderate along north- and east-facing beaches from this afternoon through the end of the workweek and possibly into the weekend. At a moderate risk, stronger or more frequent rip currents can occur, particularly at beaches exposed to the incoming swell. Before entering the water, check local beach conditions and avoid areas where rip currents or dangerous surf are observed. Thunderstorms may also develop each afternoon, bringing lightning and rapidly changing weather conditions. If thunder is heard, leave the beach and water immediately and seek safe shelter. .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. |