textproduct: San Juan

KEY MESSAGES

Issued at 225 PM AST Sun Jan 4 2026

* The risk of flooding increases from Monday into Tuesday across Puerto Rico, particularly during the afternoon and evening hours, with a limited risk of lightning as a front and an upper- level trough influence the region.

* Across the US Virgin Islands,the potential for shower activity will increase from Monday through early Tuesday morning, followed by a drier trend for the remainder of the week.

* A moderate risk of life-threatening rip currents will persist the rest of today along north- and east- facing beaches. A high rip current risk is expected by the middle of the week as a longer- period northeasterly swell reaches the local waters, affecting beaches facing the same direction in PR and the USVI.

Short Term(This evening through Tuesday)

Issued at 225 PM AST Sun Jan 4 2026

Calm weather conditions prevailed across the islands today. A few occasional showers moved across the USVI and eastern PR. Clear skies were observed early in the morning, with cloudiness increasing late in the morning into the afternoon. Temperatures ranged from the mid-80s in windward areas to the upper 80s in leeward areas, while mountain areas recorded temperatures in the upper 70s to low 80s. Winds were from the southeast at 5 to 15 mph.

A mid- to upper-level ridge will persist through Sunday, promoting dry air and subsidence aloft, as indicated by the JSJ 04/12Z sounding, which shows dry conditions above 650 mb. This pattern will generally limit widespread deep convection. At the surface, southeast winds driven by high pressure over the central Atlantic will continue. By Monday afternoon into Tuesday, a mid- to upper- level trough approaching from the western Atlantic will increase instability across the region. Surface winds will shift from east- southeast to southerly, then turn northerly as a cold front and pre-frontal trough approach, promoting moisture pooling over Puerto Rico and the US Virgin Islands.

Later this afternoon, local effects will drive showers mainly across northwest Puerto Rico. The advection of passing showers may continue overnight into early Monday across the USVI and the windward locations in PR.

Regarding hazards, today may bring periods of moderate to locally heavy rain across northwest and north-central Puerto Rico, with ponding on roads and poorly drained areas. On Monday afternoon and evening, an elevated risk of flooding rains is expected the Cordillera Central, spreading into the coast of Puerto Rico, with a limited risk of thunderstorms. The US Virgin Islands will have a limited risk of excessive rainfall. A limited lightning risk exists across Puerto Rico and the US Virgin Islands from Monday afternoon into early Tuesday, decreasing on Tuesday. By Tuesday, excessive rainfall risk should be limited and focused mainly over interior and southeastern Puerto Rico.

The frontal boundary has a good chance of crossing the islands during the early morning hours of Three Kings Day (Tuesday), followed by a somewhat drier, cooler air mass in the afternoon.

Long Term(Wednesday through next Saturday)

Issued at 247 AM AST Sun Jan 4 2026

Compared to the earlier part of the week, drier and more stable conditions are expected to return during the long term period. After the frontal passage, a downward trend in the precipitable water content is expected, as PWAT values drop to near 1 inch by Wednesday, well below seasonal values, and remain in the 50th percentile for the rest of the period. This is due to a ridge pattern building from the western Atlantic early in the period, and a TUTT-low developing northeast of the region during the weekend. The driest period is expected between Wednesday and Thursday, with the latest GFS guidance suggesting low-to mid-level RH values of 10-40%, which are within the 25th-50th percentile. Therefore, a very dry layer is expected to suppress cloud/shower development in general. Thereafter, moisture content slowly recovers between 1.25-1.40 inches, mostly due to shallow patches of moisture arriving with the trade winds, and favoring isolated to briefly scattered showers across the windward areas of the islands during the nighttime.

Minimum temperatures could reach the mid 50s across the higher elevations of PR during the early morning hours of Wednesday and once again on Thursday. Mostly due to the expected clear nights and a northeasterly component in the winds. Across coastal areas, lows are expected to range from the upper 60s to low 70s. Maximum temperatures should range from the mid-70s across the higher elevations to the mid-80s across coastal areas.

AVIATION

(18Z TAFS) Issued at 225 PM AST Sun Jan 4 2026

VFR conditions will prevail across all TAF sites during the period. However, SHRA/+SHRA will form across the PR-NW quadrant this afternoon. Most of the activity should remain in the VCTY of local terminals and will dissipate by the evening. Improving conditions overnight into early Monday morning. However, unsettled weather will possibly impact the region from 05/15z onward due to SHRA/TSRA. Winds will continue under sea breeze influence mainly from the SE at 10-15 kt with higher gusts, becoming calm to light and VRB during the overnight hours (23-13z) each day. Winds will turn from the N-NE after 05/15z.

MARINE

Issued at 225 PM AST Sun Jan 4 2026

A surface high pressure over the central Atlantic into the northeast Caribbean, maintaining light to moderate east-southeast winds across the regional waters through early Monday. A frontal boundary with an associated polar trough approaching the local waters will promote light northerly to northeasterly winds and an increase in showers and thunderstorm activity late Monday into Tuesday. Pulse of a longer-period northeasterly swell expected to arrive by midweek will lead to deteriorating marine conditions, particularly across the exposed Atlantic waters and the Caribbean Passages. Small craft operators should continue to monitor forecasts for potential changes in marine conditions.

BEACH FORECAST

Issued at 225 PM AST Sun Jan 4 2026

A moderate risk of life-threatening rip currents is expected for the rest of today along the north- and east-facing beaches of Puerto Rico, including Culebra. The rip current risk is forecast to decrease to low on Monday. The risk will increase again to moderate on Tuesday, followed by a high rip current risk on Wednesday and Thursday along north-facing beaches of Puerto Rico and the US Virgin Islands, as a long period northeasterly swell affects the Atlantic Coastline. A moderate rip current risk is expected to persist along these exposed beaches for the remainder of the week. Thus, beachgoers are urged to exercise caution, as life-threatening rip currents remain possible, particularly along exposed north- and east-facing beaches. Elsewhere across Puerto Rico and the US Virgin Islands, the rip current risk is expected to stay low through much of the week.

SJU WATCHES/WARNINGS/ADVISORIES

PR...None. VI...None. AM...None.