137 FXCA62 TJSJ 040706 AFDSJUArea Forecast Discussion National Weather Service San Juan PR 306 AM AST Sat Oct 4 2025
.KEY MESSAGES...
* A strong, long-period northerly swell will continue to produce hazardous marine and beach conditions across the islands through at least early next week. A Coastal Flood Advisory, Small Craft Advisories, Rip Current Statements, and High Surf Advisories remain in effect.
* Showers and thunderstorm activity is expected this afternoon over portions of central and northwestern Puerto Rico, enhancing the flooding and lightning threat across the area. If thunder roars, stay indoors.
* Across the U.S. Virgin Islands, passing showers will move occasionally over the region through the afternoon hours.
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.SHORT TERM...Today through Monday...
Conditions were mostly tranquil during the night hours. Some showers manage to form in the vicinity of the Virgin Islands and eastern Puerto Rico, but accumulation over land was very little. Skies were mostly clear.
The trade winds are still weak, with a steering flow now shifting from the southeast and at 4 to 8 kts. The winds will increase just a bit on Sunday and Monday, but still around 8 to 11 kts. At the upper levels, an upper level low will maintain some instability in the area, and this feature will linger into early in the workweek. Moisture is a little below normal today, but it is expected to increase toward more normal values on Sunday, and even a little more on Monday due to an approaching tropical wave. In general, the pattern will favor afternoon showers along the Cordillera Central and western Puerto Rico today and Monday. Showers could also stream from El Yunque toward the San Juan metro area. The risk of flooding will be elevated with a medium chance of these areas experiencing urban and small stream flooding. Some lightning strikes will be possible too. In the Virgin Islands, as well as some sections of eastern Puerto Rico, passing showers will be on the increase by late Sunday and Monday. While flooding is not really anticipated, ponding of water and wet roads can still be expected.
.LONG TERM...Tuesday through Saturday...
The forecast period starts with a wet and unstable pattern due to the influence of an upper-level low over the region. By Tuesday, the convergence of this low with an approaching weak tropical wave is expected to enhance the potential of convective activity, specifically showers and thunderstorms, across the U.S. Virgin Islands and Puerto Rico. High atmospheric moisture will sustain the showers and thunderstorm activity through Tuesday evening, with PWAT content near-to-above-normal (2.00 to 2.25 inches). A noticeable change is anticipated for Wednesday, as a departing upper-level low allows drier air to move in, causing PWAT values to fall to the 1.50 to 1.75 inch range. Looking ahead to Thursday, local conditions will become dependent on the evolution of a tropical wave currently near the coast of Africa.
Regarding the potential system, the National Hurricane Center (NHC) has given this wave a medium formation chance (50%) over the next 7 days. Although the latest model guidance indicate increasing moisture by the weekend, the system`s eventual trajectory and intensity remain highly uncertain. All residents and visitors must continue to track the progress of this system as it moves westwards over the Atlantic Ocean.
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.AVIATION... (06Z TAFS)
Mainly VFR conditions expected to prevail through the forecast period. After 17-19Z, SHRA and TSRA are expected to develop along the Cordillera Central. These showers should reach the PR terminals, causing periods of reduced VIS and low ceilings. VCSH are expected for VI terminals, but impacts to operations are expected to be minimal. Winds are light, out of the E to ESE at 2-8 kts.
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.MARINE...
A col near the region will promote a light to gentle variable wind flow across the islands for the next few days. A long-period north to northwesterly swell will spread across the local Atlantic waters and passages through early next week, deteriorating marine and coastal conditions through early next week. A tropical wave will approach the region by Monday, increasing the frequency of showers.
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.BEACH FORECAST...
A strong, long-period northerly swell will continue to produce hazardous beach conditions through at least Monday night along the Atlantic exposed beaches, including from western to northeastern Puerto Rico, Culebra, Vieques, and the U.S. Virgin Islands. As a result, there is a high risk of life-threatening rip currents in the aforementioned areas.
A Coastal Flood Advisory is in effect for all the Atlantic exposed beaches of the islands through Saturday evening. In addition, a High Surf Advisory is in effect for these areas through Monday morning. Please refer to our Coastal Hazard Message (CFWSJU) for additional details. Residents and visitors are urged to monitor the beach forecast and follow the beach flag warning system. Beachgoers, do not risk your life, it`s better to stay out of the water throughout the upcoming weekend!
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.SJU WATCHES/WARNINGS/ADVISORIES... PR...Coastal Flood Advisory until 6 PM AST this evening for PRZ001- 002-005-008.
High Rip Current Risk through Tuesday afternoon for PRZ001-002- 005-008-010-012-013.
High Surf Advisory until 6 AM AST Monday for PRZ001-002-005-008- 010-012.
High Rip Current Risk through this afternoon for PRZ011.
VI...High Rip Current Risk through Tuesday afternoon for VIZ001.
High Surf Advisory until 6 AM AST Monday for VIZ001.
High Rip Current Risk from 6 AM AST this morning through Tuesday afternoon for VIZ002.
AM...Small Craft Advisory until 6 PM AST Monday for AMZ711-712-716- 723-741-742.
Small Craft Advisory until midnight AST tonight for AMZ745.
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ERG/GRS
NWS SJU Office Area Forecast Discussion