Leeward Islands Offshore Forecast
| Today...E Winds 15 To 20 Kt. Seas 6 To 9 Ft In Ne To E Swell. |
| Tonight...E Winds 15 To 20 Kt. Seas 6 To 8 Ft In Ne To E Swell. |
| Thu...E Winds 10 To 15 Kt In The Caribbean, And E 15 To 20 Kt In The Atlc. Seas 6 To 8 Ft In Ne To E Swell. |
| Thu Night...E Winds 10 To 15 Kt. Seas 6 To 8 Ft In Ne To E Swell. |
| Fri...E To Se Winds 10 To 15 Kt. Seas 5 To 7 Ft In Ne To E Swell. |
| Fri Night...E To Se Winds 10 To 15 Kt. Seas 3 To 5 Ft In The Caribbean, And 5 To 7 Ft In The Atlc. |
| Sat...E To Se Winds 10 To 15 Kt. Seas 2 To 4 Ft In The Caribbean, And 5 To 7 Ft In The Atlc. |
| Sat Night...E Winds 10 Kt. Seas 2 To 4 Ft In The Caribbean, And 5 To 7 Ft In The Atlc. |
| Sun...E Winds 10 Kt. Seas 4 To 6 Ft In Ne To E Swell. |
| Sun Night...Ne To 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 134am AST Wednesday Mar 18 2026 .Short Term(Today through Friday)... Issued at 130am AST Wednesday Mar 18 2026 A relatively dry and breezy pattern will continue across the region today. Minor concentrations of Saharan dust may lead to hazy skies today. Low-level winds remain elevated early this morning but will gradually decrease from around 15 to 20 knots down toward 15 knots by this evening. Trade winds will continue to bring pockets of dry/moist air at times through Thursday. Therefore, with limited moisture and breezy conditions, shower activity will be minimal; ensemble rainfall models for today indicate light accumulations, generally under a quarter of an inch, favoring eastern and southeastern Puerto Rico, and the U.S. Virgin Islands. The precipitable water content is expected to fluctuate between 1.00 and 1.25 inches through tomorrow. However, by late Thursday, a transition begins as steering winds weaken significantly and moisture slowly rebounds. The 925 mb winds will drop to around 10 knots, and PWAT (Precipitable Water) values are expected to climb near 1.50 inches. Therefore, this lighter wind regime and increasing moisture will support afternoon shower development, predominantly over western and northwestern Puerto Rico, where hi-res ensemble model guidance suggests localized rainfall accumulations potentially reaching up to an inch. At the same time, lighter rainfall accumulations are expected across the USVI and the rest of Puerto Rico. Heading into Friday, a substantial surge in deep moisture is expected, with PWAT (Precipitable Water) nearing 1.75 inches and mid-level relative humidity spiking to near 80 percent. A prefrontal trough developing over and just north of the region will promote lighter winds, around 5 knots, and more southeasterly winds. Warmer to hot temperatures are expected, compared to previous days, and stronger afternoon showers can develop over the northwest quadrant of PR, where the slow-moving showers will enhance the flood threat. .Long Term(Saturday through Wednesday)... Issued at 130am AST Wednesday Mar 18 2026 No major changes were introduced to the long-term forecast, with unsettled conditions expected over the upcoming weekend. A deep- layered trough with an associated frontal boundary is still forecast to approach the local area by Saturday, inducing a prefrontal trough that should increase shower activity and potential for isolated thunderstorms. From the deterministic guidance of the GFS (Global Forecast System) and ECMWF, there’s a medium chance of PWAT (Precipitable Water) values increasing to above climatological normal (1.6 - 1.8 inches), with a low chance of reaching 2.0 inches. Additionally, ensemble members are tending to higher low to mid-level moisture content. Model guidance keeps to suggest that winds will likely weaken and remain variable as the frontal boundary approaches and a col region moving across the CWA. As mentioned in the previous discussion, any shower development could become stationary and produce higher rainfall accumulations. Due to the influence of the trough, slightly cooler than normal 500 mb temperatures (between -8.5 and -9 degrees Celsius), a jet streak in the upper levels (between 70 and 80 knots), and divergence aloft, allowing cloud growth and ventilation. Given the expected favorable conditions, deep convection is expected Saturday afternoon over the mountain ranges of Puerto Rico, with showers and isolated thunderstorms resulting in urban and small streams flooding. As winds gradually increase and become from the NE, an advective pattern should persist on Saturday night into Sunday morning, increasing frequency of showers over windward sections of the islands. These areas can expect ponding of water over roadways and poorly drained areas. Afternoon convection on Sunday afternoon will mostly concentrate over the mountain ranges into south/southwestern portions of Puerto Rico, with an elevated risk of flooding as well. A surface high pressure migrating into the western Atlantic on Monday, but there’s uncertainty as global solutions have discrepancies. The GFS suggests moisture content enough for the development of shower activity in the 1000 - 700 mb layer, while the ECMWF (European Centre for Medium-Range Weather Forecasts) shows drier than normal conditions. Due to local effects, shower development cannot be ruled out, the flooding threat should remain limited on Monday and none for the rest of the forecast. Residents and visitors are encouraged to continue to monitor the weather forecast, as uncertainty remains high for the next workweek. Marine Issued at 130am AST Wednesday Mar 18 2026 The pressure gradient across the region will gradually weaken through the rest of the week. However, moderate to fresh easterly winds will persist across the regional waters today. As a result, mariners can expect choppy to rough seas across much of the local waters, with Small Craft Advisories remaining in effect for most of the regional waters. A frontal boundary moving eastward along the eastern seaboard will approach the northeastern Caribbean later in the week, further relaxing the pressure gradient from Thursday through the end of the workweek. Beach Forecast Issued at 130am AST Wednesday Mar 18 2026 Beach conditions will remain hazardous for inexperienced swimmers across much of the local islands. Breezy to windy easterly winds will continue to generate choppy to rough seas across the regional waters, increasing wave action along exposed beaches. As a result, a high risk of rip currents will persist along many exposed beaches in Puerto Rico and the U.S. Virgin Islands through much of the week. Beachgoers should exercise caution, remain aware of changing coastal conditions, and monitor the latest forecasts and statements. For additional information, visit: weather.gov/beach/sju Fire Weather Issued at 130am AST Wednesday Mar 18 2026 The fire danger today will remain relative low as brief surge in low-level moisture is cross the islands this morning. This could keep relative humidities from dropping to critical fire weather thresholds. However, breezy conditions will continue along the southern coast of PR, where KBDI values remain well above critical levels, particularly in Cabo Rojo at 689. .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through Thursday afternoon for PRZ001>003- 005-008-012-013. High Rip Current Risk through this afternoon for PRZ007-011. VI...High Rip Current Risk through Thursday afternoon for VIZ001-002. AM...Small Craft Advisory until 6pm AST Thursday for AMZ711. Small Craft Advisory until 6pm AST this evening for AMZ712-716- 723-726-733-735-741. |