textproduct: San Juan

KEY MESSAGES

Issued at 531 AM AST Sat Dec 20 2025

* A northeasterly long period swell and increasing northeasterly winds will deteriorate marine and coastal conditions during the weekend.

* A High Risk of Rip Currents will return this afternoon across the northern exposed beaches of Puerto Rico and Culebra, as well as eastern St. Croix throughout the weekend.

* A Small Craft Advisory will be in effect this afternoon for the offshore Atlantic waters, and then tonight for the Anegada Passage, and throughout the weekend.

* Mainly fair weather will persist this weekend with passing showers over windward sectors of PR and the USVI, with afternoon showers possible mainly over interior to WSW PR.

* Moderate to high rain chances are forecast by mid week next week. Residents and visitors are encouraged to stay tuned to the forecast updated as there is still uncertainty.

Short Term(Today through Monday)

Issued at 531 AM AST Sat Dec 20 2025

Current satellite derived Precipitable Water (PWAT) imagery indicate patches of moisture with up to 1.45 in, steered by northeasterly flow, moving in to the region. This has resulted in light to moderate passing showers over the local waters and moving into the eastern region. Since midnight, radar accumulations over eastern Puerto Rico has resulted in up to isolated amounts of around a quarter on an inch. On the other hand, minimal accumulations were detected by radar over the USVI. Patchy fog was observed over areas of the interior. Lows were in the upper 50s and low 60s across higher elevations of PR, to the upper 60s and mid 70s across lower elevations of the PR, to the low to mid 70s across lower elevations of the USVI.

With moderate to fresh northeasterly flow continuing throughout the period, patches of moisture and drier air will filter into the region leaving PWAT values at generally normal values for this time of the year. This available moisture will mostly be confined to the lower levels, as a mid to upper level ridge continues over the region to start the short term period. This ridge will continue to provide stability and limit shower development. The ridge will gradually weaken to end the short term period and into the long term period as a polar trough starts to exit from eastern CONUS. Nevertheless, the above mentioned patches of moisture will continue to bring passing showers with generally minor accumulations over windward areas of the islands during the morning and overnight hours. Limited afternoon convection also continues to be possible each day for mainly west/southwest PR due to local and diurnal effects. Flooding risks will be limited, with mainly ponding of water over roadways and poorly drained areas. 925 mb temperatures will be at seasonal values, highs will be in the mid to upper 80s across lower elevations of the islands, with isolated/urban areas a bit higher. Lows will remain similar to tonight, with patchy fog developing over areas of the interior.

Long Term(Tuesday through Saturday)

Issued at 531 AM AST Sat Dec 20 2025

By the beginning of the long term, an upper-level trough tied to the subtropical jet stream will bring cooler mid-level temperatures as the mid-level ridge weakens and moves westward. Patches of low level moisture will continue to move across the area, resulting in isolated to scattered showers over windward sections of Puerto Rico and the U.S. Virgin Islands, mainly during the night and morning hours. By late morning into the afternoon, a moderate chance of scattered showers, around 50 percent, is expected across interior and western Puerto Rico with low chances of flooding concerns.

For Wednesday and Thursday, Christmas Eve and Christmas Day, atmospheric instability will increase somewhat as 500 mb temperatures continue to cool further to below normal values between -8 and -10 degrees Celsius. A polar trough will extend southward into the Caribbean, while an additional upper-level trough will interact with a surface frontal boundary north of the region. The frontal boundary will move close to the area or cross the region, allowing a slight increase in moisture, while enhanced upper-level divergence. However, the global models have been somewhat unstable from run to run, but the latest guidance is now indicating less available moisture compared to yesterday. Precipitable water (PWAT) values are trending closer to seasonal levels, generally around 1.5 to 1.6 inches. Although some uncertainty remains, the reduction in moisture has led to a slight downward adjustment in rain chances. A moderate chance (around 50%) is expected for scattered showers with isolated thunderstorms. Galvez-Davison Index values have also lowered, suggesting reduced instability and supporting only a few isolated thunderstorms, with convection remaining mostly shallow.

Friday and Saturday, models are suggesting drier-than-normal air, leading to stable weather. Cooler temperatures are expected during the holiday period, as indicated by a trend toward below normal 925 mb temperatures.

AVIATION

(06Z TAFS) Issued at 531 AM AST Sat Dec 20 2025

VFR conditions prevailing during the period. Passing -SHRA at or in the VCTY of TJBQ/TJSJ/TIST/TISX to start the period. -SHRA/SHRA then forming over interior to WSW PR, near TJPS/TJBQ, by 20/17 - 23Z. Winds picking up again from the ENE after 10/13Z will be calm to light and variable through this morning, then will return from the ENE after 19/13z at 15 - 20 kts, with higher gusts and sea breeze variations.

MARINE

Issued at 531 AM AST Sat Dec 20 2025

Moderate to locally fresh east to northeast winds will continue for the next few days. A long-period northerly to northeasterly swell, generated by a surface low over the central Atlantic, will promote hazardous seas for small craft from this afternoon through at least late Sunday, particularly across the Atlantic waters and Anegada passage. Small Craft Advisories are in effect from noon today due to seas gradually building up to 7 feet.

BEACH FORECAST

Issued at 531 AM AST Sat Dec 20 2025

Today, there is a moderate risk of rip currents along the north- facing beaches of Puerto Rico and the U.S. Virgin Islands. A moderate risk means that life-threatening rip currents are possible within the surf zone. This afternoon, the risk is expected to increase to high as beach conditions deteriorate due to strengthening winds and another northerly swell spreading across the local Atlantic waters, leading to large breaking waves. The high risk will likely extend throughout the entire weekend. Beachgoers are urged to strictly follow guidance from lifeguards, beach patrol flags, and posted signs. Stay tuned to the forecast and exercise caution at the beaches.

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk from this evening through late Sunday night for PRZ001-002-005-008-012.

VI...High Rip Current Risk from this evening through late Sunday night for VIZ002.

AM...Small Craft Advisory from noon today to 6 PM AST Sunday for AMZ711.

Small Craft Advisory from 6 PM this evening to 6 PM AST Sunday for AMZ723.