textproduct: San Juan

KEY MESSAGES

Issued at 500 AM AST Sat Dec 27 2025

* Pulses of long-period northerly swell will maintain hazardous marine conditions today, especially across Atlantic waters and local Caribbean passages. Current and additional swell pulses will also sustain a life-threatening rip current risk along north- facing beaches of Puerto Rico, Culebra, and the northern U.S. Virgin Islands through at least Sunday. High surf risks will persist through this afternoon at exposed shores. While conditions may gradually improve thereafter, additional swell pulses early next week may once again deteriorate marine and beach conditions.

* Overall weather conditions will remain mostly quiet, with brief passing showers at times and little to no thunderstorm activity expected. A slight increase in shower activity and a low chance of isolated thunderstorms is possible mid- to late week as a short-wave trough and a weak surface-induced trough approach the region, though impacts are expected to remain localized.

* U.S. Virgin Islands: Weather conditions will remain generally stable, with passing showers at times and no thunderstorm potential, even during the midweek period. No significant inland weather impacts are anticipated.

* New Years Eve: Showers may become more frequent, especially across western Puerto Rico, with a low chance of isolated lightning. Forecast confidence is moderate, as model guidance continues to fluctuate.

Short Term (Today through Monday)

Issued at 500 AM AST Sat Dec 27 2025

Clear skies were observed across Puerto Rico and the Virgin Islands during the night hours. It was very cool too, with some stations reporting lows in the upper 50s at higher elevations, and the mid 60s to low 70s elsewhere.

Satellite-derived precipitable water imagery show very dry air across the region, with values of only 0.75 inches, which is well below the normal value for this time of year. At the surface, high pressure is centered over the western Caribbean, and a polar trough is covering most of the Atlantic Ocean. This is causing a weak steering flow across the local islands, coming out of the northeast today at 4 to 7 kts, less than 4 knots tomorrow, and from the east at 5 to 7 kts on Monday. Also, the high will maintain very low relative humidities at the mid levels, with a trade wind cap inversion at 850 mb. Under these conditions, heavy showers are not expected to develop, but local effects may still trigger some showers along the interior and western Puerto Rico. Impacts are expected to be very limited, possibly with ponding of water and wet roads.

Temperatures will remain very comfortable too, with 925 mb values at one to two standard deviations below normal. For mountains: expect lows in the 50s and 60s, and highs in the low 70s. For low elevations and coastal areas: expect lows in the 60s and low 70s, and highs in the low 80s.

Long Term (Tuesday through Saturday)

Issued at 419 AM AST Sat Dec 27 2025

From Tuesday through Thursday, a dry and stable winter pattern will dominate, supported by post-frontal dry air pushing southward and weak mid-level ridging. This will favor mostly fair weather, limited shower activity, and cooler nighttime temperatures typical for this time of year. During this same period, an eastward-moving surface high north of the region will mainly influence the wind pattern, maintaining a gentle to moderate east-southeast breeze through Thursday.

A slight transition is expected later in the period as a short- wave trough approaches from the west. Although the latest guidance indicates its axis will remain west of the islands, it will still influence the region by weakening the mid-level ridge and supporting the development of a weak surface trough late Friday into Saturday. This setup may allow moisture to shift back toward the area, with the highest sensitivity across western Puerto Rico and the Mona Passage, while other areas experience more limited effects.

From Wednesday night into Saturday, showers may become more frequent in favored areas, especially across western and interior Puerto Rico and exposed coastal locations, with a few periods of locally heavy rainfall possible. A low chance of isolated thunderstorms exists late Friday into early Saturday, mainly over western Puerto Rico and nearby waters, producing brief heavy rain, gusty winds, and lightning. Winds are expected to weaken and become more variable late Friday into Saturday due to the surface trough, which may support a warmer-than-normal feel on Friday, particularly during the afternoon. Forecast confidence is moderate, as moisture fields continue to shift and guidance oscillates between wetter and drier solutions. This variability is not necessarily negative, as New Years Eve currently trends drier with generally favorable conditions, though marine and beach hazards may continue.

AVIATION

(06Z TAFS) Issued at 500 AM AST Sat Dec 27 2025

VFR conditions expected to prevail through the forecast period. SHRA is expected after 17Z for TJPS, with brief periods of reduced VIS and low ceilings. After 22Z, VCSH are expected for TJSJ and USVI terminals, but impacts are expected to be limited. Winds will be from the ENE from 5-9 kts, becoming light and variable after 22Z.

MARINE

Issued at 500 AM AST Sat Dec 27 2025

A surface high pressure system over the western Atlantic will maintain light to moderate east to northeast winds across the local waters over the next few days. Meanwhile, pulses of long- period northerly swell will continue to spread into the region, maintaining hazardous marine conditions. Small Craft Advisories remain in effect through this afternoon, with rough seas persisting afterward as the swell gradually diminishes. Looking ahead, additional pulses of northerly swell are expected early next week, which may bring another round of hazardous conditions for small craft across the local waters.

BEACH FORECAST

Issued at 500 AM AST Sat Dec 27 2025

A High Rip Current Risk remains in effect through tonight along north-facing beaches of Puerto Rico, Culebra, St. Thomas, and St. John, while a High Surf Advisory remains in effect through 6 PM this evening for the north coast of Puerto Rico. Recent buoy observations (NE Puerto Rico buoy 41043) confirm additional pulses of long-period northerly swell, bringing seas of 78 feet with periods of 1213 seconds across the local Atlantic waters and Caribbean passages. These conditions support the potential for breaking waves exceeding 10 feet at exposed beaches, reinforcing dangerous and life-threatening swimming conditions today.

Beachgoers are strongly urged to stay out of the water at north- facing beaches, especially at unguarded locations, and to follow all beach flag warnings and coastal advisories. For additional details and the latest updates, refer to the Coastal Hazard Message (CFWSJU).

FIRE WEATHER

Issued at 500 AM AST Sat Dec 27 2025

Drying conditions continue to develop, especially across southern Puerto Rico, where localized abnormally dry conditions persist. Monthly rainfall has been minimal, and 30- to 60-day rainfall deficits continue, supporting the ongoing drying of fine fuels.

There is no elevated fire danger today. While there is some uncertainty in drought and soil moisture indices, KBDI values have increased to around 540 at Cabo Rojo and 503 at Camp Santiago, indicating increasing fuel dryness, though still below thresholds for Fire Weather Statement or Red Flag Warning. Low relative humidity at times, combined with occasional wind gusts of 2025 mph typical of winter trade-wind patterns, has briefly enhanced fire spread potential, with a few small wildfires observed. Overall, fire danger remains low at present, but continued drying over the next several days to weeks could elevate fire risk, warranting close monitoring, particularly across southern Puerto Rico.

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk through late Sunday night for PRZ001-002- 005-008-010-012.

High Surf Advisory until 6 PM AST this evening for PRZ001-002- 005-008-010.

VI...High Rip Current Risk through late Sunday night for VIZ001.

AM...Small Craft Advisory until 6 PM AST this evening for AMZ711-712- 716-723-741-742.