textproduct: San Juan

KEY MESSAGES

Issued at 115 PM AST Tue Dec 30 2025

* The risk of lightning and localized flooding will increase from New Year's Eve into Thursday as an upper-level trough and associated frontal boundary approach from the west.

* For the U.S. Virgin Islands, although the approaching upper- level trough is expected to increase the chance of showers and thunderstorms across the forecast area, organized convective activity is expected to remain well west of the USVI.

* Life-threatening rip currents will continue to prevail across the north-facing beaches of Puerto Rico, Culebra, and the northern U.S. Virgin Islands.

Short Term(This afternoon through Thursday)

Issued at 115 PM AST Tue Dec 30 2025

The short-term forecast remains on track, with the chance of showers and thunderstorms increasing by the end of the period (Wednesday into Thursday) as an upper-level trough and its associated frontal boundary approach from the west. As this feature moves closer to the forecast area, falling heights, decreasing mid-level temperatures, and increasing moisture advection are expected, with precipitable water values reaching up to 2.0 inches. Despite this scenario, the latest guidance continues to suggest that the highest moisture content and organized convective activity remain west of the forecast area.

As a result, under this evolving pattern, limited shower activity is expected to continue, with isolated passing showers across the north and east coastal areas of Puerto Rico, and the US Virgin Islands tonight and Wednesday morning. By Wednesday afternoon, showers will develop over the western interior of Puerto Rico, with limited shower activity elsewhere. An isolated thunderstorm cannot be ruled out across western areas tomorrow afternoon.

The chance for showers and thunderstorms will increase Wednesday night into Thursday, with showers and isolated thunderstorms reaching the regional waters, particularly the Mona Passage and Atlantic waters. Some of these showers may reach the western half of Puerto Rico. Under an east-southeast wind flow, passing showers are also expected across the eastern coastal areas of Puerto Rico and the U.S. Virgin Islands. By Thursday afternoon, if breaks in cloud cover develop, afternoon convection is expected in northwest Puerto Rico. Therefore, there is an increasing risk of lightning and minor flooding across the forecast area on Wednesday and Thursday.

Pleasant temperatures will continue to prevail. At lower elevations, maximum temperatures are expected to range from the low to mid-80s, while minimum temperatures are expected to range from the upper 60s to the low 70s.

Long Term (Friday through next Tuesday)

Issued at 401 AM AST Tue Dec 30 2025

An unstable weather pattern will persist on the first day of the long term, as the main weather pattern is dominated by a mid- to upper-level trough. This upper-to mid-level feature will create a very unstable weather pattern, enhancing colder temperatures at 500 MB, ranging from -8 to 9 degrees. Meanwhile, at the surface, moisture from a sinking frontal boundary over the Caribbean and instability from the pre-frontal trough will align perfectly with the upper instability, increasing the frequency and coverage of showers during the day. Given the variability of winds due to weakening of the pressure gradient resulting from the surface pre- frontal trough, the coverage and movement of showers will be slow and widespread across the mountain sections. Upper conditions will rapidly improve as the subsidence side of the upper-level trough moves eastward, and a more stable condition will dominate. At 500 MB, a ridge will move in, warming temperatures from -9 to -5 degrees. Stable conditions will persist from Saturday into Monday; however, at the surface, shallow patches of moisture dragged by the east-southeasterly wind flow will allow some showers in the morning across the eastern side and across the interior and western Puerto Rico for the afternoon. There are some discrepancies in the amount of available moisture (relative humidity %) on those days, with the ECMWF calling for a wetter, more seasonal pattern.

On Tuesday again, weather conditions will deteriorate as another upper-level trough moves into the Caribbean. Combined with the instability, values of Relative humidity between 700 and 300 MB show an increase in moisture, which will induce a more showery pattern.

AVIATION

(18Z TAFS) Issued at 115 PM AST Tue Dec 30 2025

Mainly VFR conds expected across all terminals during the forecast period. Passing showers will result in VCSH for TJSJ aft 30/23Z. Winds from the ESE will become light and VRB after 30/23Z, increasing from the SE btwn 8-12 kt, with higher gusts and sea breeze variations aft 31/13-14Z.

MARINE

Issued at 115 PM AST Tue Dec 30 2025

An east-to-southeast wind flow is expected to continue as a frontal boundary approaches from the west, increasing the potential for showers and thunderstorms. Pulses of long-period northerly swell will persist across the Atlantic waters and passages.

BEACH FORECAST

Issued at 115 PM AST Tue Dec 30 2025

Pulses of northerly swell will continue to propagate across the regional waters, resulting in a high to moderate risk of rip currents along north-facing beaches of Puerto Rico, Culebra, St. Thomas, and St. John during the next few days.

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk through Wednesday afternoon for PRZ001-002- 005-008-012.

High Rip Current Risk until 6 PM AST this evening for PRZ010.

VI...High Rip Current Risk through late tonight for VIZ001.

AM...None.