textproduct: San Juan

KEY MESSAGES

Issued at 537 AM AST Tue Dec 23 2025

* The short-term weather pattern remains largely unchanged, with unstable conditions expected from December 24 through December 25 for the region.

* A limited flooding threat is expected through Thursday, mainly ponding of water over roadways and poorly drained areas for PR and the USVI.

* Marine and beach conditions will gradually deteriorate today and tomorrow; these conditions will continue throughout the week as pulses of northerly swell arrive. Small Craft Advisories and High Risk of Rip Currents will soon be in effect.

Short Term(Today through Thursday)

Issued at 537 AM AST Tue Dec 23 2025

Overnight conditions were relatively calm, with pockets of passing showers over the regional waters, some of which reached northern and eastern sections of eastern Puerto Rico. Temperatures remained cool, with readings in the 60s across the higher elevations and in the 70s across urban and coastal areas. The prevailing wind flow was from the northeast at 5 to 10 mph, with occasional higher gusts near passing showers.

The overall short-term weather pattern has not changed significantly, therefore much of the previous discussion remains valid. From December 24 through December 25, atmospheric conditions will remain unstable due to the continued influence of a polar trough at upper levels. Mid-level temperatures between 700 and 500 mb are expected to remain around 10 degrees Celsius, which is at or below the 10th percentile for this time of the year. This anomalously cold air aloft will support steep lapse rates and increased instability. In addition, favorable jet dynamics will overspread the forecast area, with a 6090 kt jet at 250 mb enhancing upper-level ventilation and increasing 0500 mb bulk shear, a pattern often associated with more organized convection. Nevertheless, the primary limiting factor will continue to be available moisture across the northeastern Caribbean. The associated frontal boundary remains northwest of the area and is forecast to gradually sag southward. Precipitable water values are expected to remain near normal to slightly below normal through Thursday. Additionally, the persistent northeasterly low-level flow will keep temperatures below normal, potentially limiting afternoon surface heating and further restricting deep convective development.

As a result, any convection that develops is expected to be localized rather than widespread. Relatively fast steering winds will continue to limit rainfall accumulations, even where heavier showers occur. Overall, expect periods of showers during the overnight and morning hours, with isolated thunderstorms developing mainly over the regional waters. Some thunderstorms may approach coastal areas, particularly across the Atlantic waters. During the afternoon hours, showers with isolated thunderstorms may develop over interior and southwestern Puerto Rico.

At this time, there is a limited flooding threat through Thursday, December 25, primarily in the form of ponding of water on roads and in poorly drained areas.

Long Term(Friday through Tuesday)

Issued at 537 AM AST Tue Dec 23 2025

Drier air behind the frontal boundary will dominate throughout the the period. Precipitable Water (PWAT) values are forecast at around to below an inch with isolated patches of moisture (PWAT up to around 1.2 in) reaching the area and promote passing showers from time to time. Although low PWAT values are forecast, upper troughs will move northeast of the area during the latter part of this week. building surface high over the western Atlantic and a frontal low over the north-central Atlantic will promote northeasterly steering flow to start the period. Model guidance suggests that winds will gradually veer to start the next week, promoting southeasterly flow by the end of the period. Under the northeasterly flow, 925 mb temperatures are forecast to be below normal. Minimum temperatures are forecast in the 50s to low 60s across higher elevations of PR, in the upper 60s to mid 70s across lower elevations of PR, and in the low to mid 70s across the USVI. Maximum temperatures are forecast around the mid 80s across lower elevations of the islands, with isolated/urban areas a bit higher. This will likely enhance patchy fog across sectors of interior Puerto Rico.

AVIATION

(06Z TAFS) Issued at 537 AM AST Tue Dec 23 2025

All TAF sites should experience VFR conditions across most terminals through the period. However, SHRA may intermittently affect TJSJ, TIST, and TISX, especially during the overnight and early morning hours. TJPS could experience VCSH after 1217Z. Winds will remain from the NE at 6-10 knots, with occasional higher gusts near passing showers.

MARINE

Issued at 537 AM AST Tue Dec 23 2025

A surface high over the western Atlantic and a frontal low over the north-central Atlantic will promote moderate east to northeast winds to start the period. A series of surface highs and frontal lows will continue moving into the Atlantic during the period, resulting in moderate to locally fresh northeast winds through at least Wednesday, becoming moderate by Thursday.

A long-period northerly swell, from the above mentioned frontal low, will arrive and spread across the offshore Atlantic waters this afternoon. This will result in choppy to rough seas, becoming hazardous for small craft. These conditions will continue throughout the week as seas build to 6 to 9 feet, spreading to the nearshore Atlantic Waters and local Passages. Another pulse of swell will arrive later in the workweek and support deteriorated conditions throughout the end of the week.

BEACH FORECAST

Issued at 537 AM AST Tue Dec 23 2025

Although the day will start with a moderate risk of rip currents for the northern and eastern coastline of Puerto Rico, as well as for exposed beaches of Culebra and the USVI, conditions will deteriorate late tonight as a northerly swell arrives. This northerly long-period swell will increase the risk of rip currents up to high for exposed northern beaches by late tonight and throughout the rest of the week. Another pulse of swell will arrive later in the workweek and support deteriorated conditions throughout the end of the week. Please continue to monitor the forecast for updates as conditions evolve.

SJU WATCHES/WARNINGS/ADVISORIES

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

VI...None. AM...Small Craft Advisory from noon today to midnight AST Thursday night for AMZ711.

Small Craft Advisory from noon Wednesday to midnight AST Thursday night for AMZ712.