textproduct: San Juan

KEY MESSAGES

Updated at 240 AM AST Sun Apr 12 2026

* Locally induced showers and thunderstorms are expected to develop once again over the interior and western portions of Puerto Rico this afternoon, where the flood threat is elevated.

* Across the US Virgin Islands, showers are expected to increase from late tonight into Monday morning.

* There is a Flood Watch for Puerto Rico and the US Virgin Islands, and will be in effect from 10 AM Monday through 8 AM Wednesday.

* A High Risk of Rip Currents remains in effect for the western, northern, and eastern coast of Puerto Rico and Culebra through Monday afternoon.

Short Term(Today through Tuesday)

Issued at 240 AM AST Sun Apr 12 2026

Clear to partly cloudy skies were observed overnight across the islands. Passing showers were noted mainly across the Anegada Passage and Caribbean waters. As of 2 AM, minimum temperatures were from the low 60s across the higher elevations of Puerto Rico to the mid 70s across the lower elevations of the islands. The wind was from the east at 10 mph or less. For the rest of the morning hours, low-level clouds with scattered showers currently over the Leeward Islands, are expected to move across portions of the USVI and eastern PR. This surge in moisture will combine with daytime heating and the sea breeze convergence to trigger the development of showers and thunderstorms along the mountain ranges of PR during the afternoon hours. Urban and small stream flooding is likely with this activity.

For Monday and Tuesday, the combination of an approaching front, a developing pre-frontal trough, and a mid-to upper-level trough will promote a moist and unstable weather pattern across the region. Satellite derived Total Precipitable Water (TPW) imagery indicates a deep moisture plume from the NW Atlantic and another developing over the eastern Caribbean. Global model guidance indicates the Precipitable Water Content (PWAT) increasing from 1.70 inches today to near 2.00 inches through Tuesday, which is above the 75th percentile for the season. Colder than normal 500 mb temperatures of -10C and -11C are also expected in response to the deep layer upper level trough. Winds will generally be light from the east to southeast over land areas, as the surface trough develops over the region. However, a northeasterly component is expected between Monday afternoon and early Tuesday morning as the front sinks further southward across the islands. This period is expected to be the most active in terms of the heaviest showers. Daily rainfall accumulations are expected to range between 1 and 3 inches with locally higher amounts. This rainfall over saturated soils will maintain an elevated threat for urban and river flooding as well as potential mudslides in areas of steep terrain. Therefore, a Flood Watch is in effect for all of PR and the USVI during this time frame.

Long Term(Wednesday through Sunday)

Issued at 240 AM AST Sun Apr 12 2026

The wet and unsettled weather pattern may extend into the long-term forecast. A surface high pressure is expected to build over the Western Atlantic, gradually increasing the pressure gradient, resulting in strengthening southeasterly to easterly winds. These conditions will bring back breezy to locally windy conditions across the coastal areas of the islands. Nevertheless, the influence of the deep-layered trough and abundant moisture content across the CWA will maintain a limited to elevated risk of flooding. From the latest model guidance, at least through Saturday, PWAT values should increase and remain above normal for this time of the year (between 1.6 and 1.8 inches, low chance for 2.0 inches). Additionally, moisture content in the low and mid levels should remain high through most of the period, with relative humidity above 60 - 70 %, and steep lapse rates in the 850 - 700 mb levels. Due to the proximity of the trough, mid level temperatures will likely remain cooler than normal (around - 8 degrees Celsius), while a jet streak in the high levels will maintain strong winds (70 - 80 kt) through Saturday, allowing ventilation and cloud growth. Additionally, the Galvez-Davison Index (GDI) suggests deep convection activity across the CWA, with isolated to scattered thunderstorms in the afternoons and the night hours. The most likely scenario, from Wednesday through Saturday, is moderate to locally heavy showers and isolated thunderstorms moving over windward sections of Puerto Rico and the U.S. Virgin Islands throughout the day, with afternoon convection over the interior into northwestern/western sections of Puerto Rico. Due to the expected weather event in the short term, saturated soils and above-normal river levels are very likely and may enhance flooding potential. Hence, the limited to elevated flooding threat remains, with a limited lightning potential. Impacts may include urban and small stream flooding, with localized flash flood, landslides, and rapid river rises. By Sunday into Monday, weather conditions should gradually improve, but there are discrepancies between global solutions for early next week as members of the GEFS are tending to wetter conditions, while ENS members are tending to a seasonal pattern.

AVIATION

(06Z TAFS) Issued at 240 AM AST Sun Apr 12 2026

Mainly VFR conditions are expected to prevail through the morning hours across all terminals. However, passing -SHRA en route fm the Leeward terminals may reach the USVI and eastern PR terminals. From 16z-22z, +SHRA/TSRA are expected to develop over the interior of PR, causing mostly VCTS across the PR terminals, with possible tempo MVFR conds at TJBQ/TJSJ. East winds between 8-14 kt with sea breeze variations expected aft 12/14z. An approaching front from the NW Atlantic waters could lead to +TSRA across the offshore Atlantic waters and Mona Passage from late tonight into Monday morning.

MARINE

Issued at 240 AM AST Sun Apr 12 2026

A broad surface high pressure across the central Atlantic and a front over the western Atlantic will promote moderate trades through the rest of the weekend. Pulses of northerly swell will continue to move through the Atlantic waters and passages, where small craft should continue to exercise caution for the next several days. Between Monday through Wednesday, the combination of the front and associated pre-frontal trough will increase showers and thunderstorms across the local waters, creating locally hazardous marine conditions. Small Craft Advisory conditions are expected across the Atlantic waters due to seas building up to 7 feet through midweek.

BEACH FORECAST

Issued at 240 AM AST Sun Apr 12 2026

A life-threatening risk of rip currents will persist through at least Monday afternoon as a pulse of northerly swell maintains a High Rip Current Risk across the north-facing beaches of Puerto Rico from the northwest through the northeast, as well as Culebra, and this risk may be extended. Across Vieques and the U.S. Virgin Islands, a moderate risk of rip currents will continue, while a low risk persists along the southern and more protected beaches of Puerto Rico. Increasing winds early to midweek could expand areas of High Rip Current Risk. Avoid the water at high-risk beaches; rip currents are likely and can be life-threatening. Sharing is saving.

HYDROLOGY

Issued at 240 AM AST Sun Apr 12 2026

As a mid-to upper-level trough approaches from the northwest, the likelihood of flooding is increasing from late tonight until at least midweek. An elevated flooding risk is forecast through this period. Showers and thunderstorms will increase in frequency on Monday, but the heaviest activity is anticipated for Monday night into Tuesday. Although a level of uncertainty is still present, the days with the highest potential for flooding are Monday and Tuesday. However, above normal moisture will persist through late in the week. The likelihood of urban and small stream flooding, isolated flash flooding, landslides and rapid river rises continues to increase. Residents and visitors are urged to remain alert to changing weather conditions and to avoid flooded roadways. A Flood Watch (FFASJU) and an Hydrologic Outlook (ESFSJU) are currently in effect to highlight this flooding potential.

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk through Monday afternoon for PRZ001-002- 005-008-010-012.

Flood Watch from Monday morning through Wednesday morning for PRZ001>013.

VI...Flood Watch from Monday morning through Wednesday morning for VIZ001-002.

AM...None.