Mona Passage Southward to 17N Marine Forecast
| Tonight...Southeast Winds Around 10 Knots. Seas 3 To 4 Feet. Wave Detail: Southeast 3 Feet At 6 Seconds And Northeast 2 Feet At 10 Seconds. Scattered Showers Until Early Morning, Then Isolated Showers Late. |
| Sunday...Southeast Winds 10 To 15 Knots With Gusts Up To 20 Knots. Seas 3 To 5 Feet, Building 4 To 7 Feet In The Afternoon. Wave Detail: Southeast 3 Feet At 6 Seconds And Northeast 2 Feet At 9 Seconds. Scattered Showers In The Morning. |
| Sunday Night...Southeast Winds 10 To 15 Knots With Gusts Up To 20 Knots. Seas 4 To 7 Feet. Wave Detail: Southeast 3 Feet At 5 Seconds And Northeast 2 Feet At 11 Seconds. |
| Monday...Southeast Winds Around 15 Knots With Gusts Up To 20 Knots. Seas 4 To 6 Feet. Wave Detail: Southeast 4 Feet At 6 Seconds And Northeast 4 Feet At 12 Seconds. |
| Monday Night...Southeast Winds 10 To 15 Knots With Gusts Up To 20 Knots. Seas 4 To 6 Feet. Wave Detail: Southeast 4 Feet At 6 Seconds And North 4 Feet At 12 Seconds. Scattered Showers. |
| Tuesday...Southeast Winds 10 To 15 Knots With Gusts Up To 20 Knots. Seas 4 To 5 Feet. Wave Detail: Southeast 4 Feet At 7 Seconds And North 3 Feet At 11 Seconds. Scattered Showers In The Morning. |
| Tuesday Night...Southeast Winds 10 To 15 Knots. Seas 3 To 4 Feet. |
| Wednesday...Southeast Winds Around 10 Knots. Seas Around 3 Feet. |
| Wednesday Night...Southeast Winds 5 To 10 Knots. Seas Around 3 Feet. Scattered Showers. |
| Thursday...Southeast Winds 5 To 10 Knots. Seas 2 To 3 Feet. |
| Thursday Night...East Winds Around 5 Knots. Seas 2 To 3 Feet. Scattered Showers. |
| Area Forecast Discussion National Weather Service San Juan PR 311pm AST Sat September 27 2025 .KEY MESSAGES... * Afternoon convection should remain through at least sunset across Puerto Rico. We urge people to find shelter if they heard a thunder or see lightning because this activity is strong and winds are moving slow * Showers will move across the U.S. Virgin Islands later today into the early hours of tomorrow. * A long period northeasterly swell from Hurricane Humberto will continue to increase seas and breaking waves during the weekend, and resulting in a high risk of rip currents. Additionally, there is a small craft advisory in effect across the offshore Atlantic waters. * An increase in moisture is forecast from Monday into Tuesday; however, Saharan dust will also move in, resulting in hazy skies in some isolated areas. .SHORT TERM...Tonight through Monday... Current satellite derived precipitable water values indicate a band of moisture with values around 1.9 to around 2 inches over the USVI and eastern Puerto Rico. This band of moisture is between Major Hurricane Humberto, over the subtropical central Atlantic around 420 miles NE of St. John, and Tropical Depression Nine, centered between eastern Cuba and the central Bahamas. Diurnal heating, sea breeze convergence and light southerly steering winds are promoting afternoon convective showers and thunderstorms over interior to northern PR, where a limited to elevated flooding risk continues. Lines of showers and thunderstorms remain possible downwind of Vieques, Culebra and the USVI. Light concentrations of Saharan Dust are also present, increasing somewhat on Monday. PWAT (Precipitable Water) values will decrease tomorrow as the current band of moisture is pulled away by the distant TCs. However, trailing moisture from Humberto will reach the islands late Sunday into Monday. This will increase PWAT (Precipitable Water) values to around 2 inches during that period. Current southerly steering flow will gradually turn more east-southeasterly by late Sunday into Monday while also increasing to around 10 to 15 kts. This moisture will be accompanied by the above mentioned Saharan Dust. Afternoon showers and thunderstorms are forecast during the short term period over the interior and steered towards northern PR tomorrow and more towards NW PR on Monday. Limited to elevated flooding risks will persist. Overnight and early morning showers are also forecast over windward sectors. Temperatures and heat indices have remained well above normal values. 925 mb temperatures are expected to continue above normal values during the short term period, with highs in the low to mid 90s at most coastal areas. Elevated to significant heat threats will persist for the short term periods, with Extreme Heat Warnings/Heat Advisories anticipated each day. Long Term Tuesday through Saturday... The long-term forecast remains on track. On Tuesday, the surface pattern will continue under the influence of Hurricane Humberto well north of the region and a strengthening surface high pressure over the central Atlantic, resulting in a weak southeasterly wind flow. Under this setup, the islands will experience brief intrusions of Saharan dust with precipitable water values near 1.6 inches, close to the 25th percentile for the year. This pattern will favor a generally stable day with calm conditions in the morning and localized afternoon activity. Similar weather will persist on Wednesday, while on Thursday precipitable water is forecast to decrease further, with global model guidance suggesting values nearly two standard deviations below normal. Relative humidity between 700–500 mb also shows a drying trend, supporting mostly stable mornings with only localized showers across the interior regions. A more unsettled pattern is expected from Friday into Saturday as global model guidance indicates an increase in instability, with 700–500 mb lapse rates steepening and 500 mb temperatures slightly decreasing to around –6 °C due to an upper-level trough extending from the western Caribbean into the islands. At the surface, a weakening of the pressure gradient is anticipated as a tropical system moves into the northwestern Atlantic, reducing the influence of the surface high pressure. This evolving pattern will induce surface convergence, enhance instability, and result in very weak steering flow. Consequently, a variable pattern is forecast, with long-lasting afternoon showers primarily affecting the interior, but drifting into different sections of the islands due to weak winds. Marine A pulse of a long period northeasterly swell from Major Hurricane Humberto will continue to increase seas across the local waters through the rest of the weekend. Buoy 41043 is reporting seas around 7 feet across the offshore Atlantic waters. As a result, a Small Craft Advisory was issued. This conditions will continue to spread into the coastal Atlantic waters and the Anegada Passage during the weekend. Therefore, the Small Craft Advisory will extend to the coastal Atlantic water later tonight into Sunday. Seas are expected to remain between 7 and 8 feet across the Atlantic waters and up to 5 feet across the Caribbean waters. Improving marine conditions are forecast from Monday as the energy from the swell diminish across the area. Beach Forecast A long period northeasterly swell from Major Hurricane Humberto will continue to increase breaking waves through the weekend. As a result, deteriorating coastal conditions are expected, especially across the northern coastal areas of Puerto Rico, including beaches along the northeast PR. For Culebra, Vieques, the U.S. Virgin Islands, and northwestern Puerto Rico, the risk will remain moderate. However, deteriorating conditions are forecast to spread to more coastal areas, including St. Croix, Culebra, and the northwestern coast of Puerto Rico, during the weekend. Improving coastal conditions are expected beginning on Monday. .SJU WATCHES/WARNINGS/ADVISORIES... PR...Extreme Heat Warning until 5pm AST this afternoon for PRZ001>005-007-008-010-011. High Rip Current Risk through late Sunday night for PRZ001-002- 005-008. Heat Advisory until 5pm AST this afternoon for PRZ012-013. VI... Heat Advisory until 5pm AST this afternoon for VIZ001-002. AM...Small Craft Advisory until midnight AST Sunday night for AMZ711. Small Craft Advisory from 6am Sunday to midnight AST Sunday night for AMZ712. Small Craft Advisory from 6am to 6pm AST Sunday for AMZ716. Small Craft Advisory from noon Sunday to midnight AST Sunday night for AMZ741. |
San Juan Radar
Southeast Radar