textproduct: San Juan

KEY MESSAGES

Updated at 317 AM AST Tue Apr 28 2026

* Showers and isolated thunderstorms are expected across the islands today, increasing the flooding and lightning risk, resulting in urban and small stream flooding, particularly across northern Puerto Rico in the afternoon.

* A moderate rip current risk continues over north and east- facing beaches Puerto Rico and the U.S. Virgin Islands for the next several days. Beachgoers should exercise caution along exposed beaches.

* Warmer-than-normal conditions will continue across urban and coastal areas of the islands, with heat indices reaching or exceeding 100F, affecting the more vulnerable communities.

Short Term(Today through Thursday)

Issued at 317 AM AST Tue Apr 28 2026

Overall, relatively calm weather conditions prevailed across Puerto Rico and the U.S. Virgin Islands under partly to mostly cloudy skies. Radar and satellite imagery captured a line of showers developing just off the southern coast of Puerto Rico during the early morning hours. While some of this activity reached the coastline between Guanica and Ponce, rainfall accumulations remained minimal. Meanwhile, additional lines of showers moved across the Caribbean Sea, remaining mostly south of St. Croix throughout the night, though a few brushed the island with little to no accumulation. Overnight low temperatures ranged from the mid to upper 70s across coastal and urban areas, while the central mountain range saw cooler temperatures in the upper 60s to low 70s. Winds remained light and variable at 5 knots or less.

For the remainder of the morning, shower frequency is expected to increase across portions of southern and eastern Puerto Rico, as well as the U.S. Virgin Islands. This is due to abundant moisture filtering into the region, which will facilitate further development. Current precipitable water values indicate above-normal moisture levels of approximately 2 inches, a trend expected to persist through at least the end of the workweek. At the surface, a high-pressure system will maintain a light southerly steering flow through Wednesday. The flow is anticipated to shift from the east- northeast on Wednesday morning before returning to the east- southeast by the afternoon as the surface high migrates from the central to the eastern Atlantic.

Throughout the rest of the period, afternoon convective activity is likely to produce moderate to heavy rainfall and thunderstorms across the interior and toward northern and northwestern Puerto Rico. This activity will be driven by the combination of deep moisture, daytime heating, and local effects. Because winds are light, these showers will move slowly and expand in coverage, persisting over the region for longer time. Therefore, the risk of flooding will be elevated today, particularly during the afternoon hours. Periods of heavy rainfall, lightning, and ponding on roadways are likely, with localized flooding possible in areas where rain persists.

Despite the anticipated rainfall, warm to hot temperatures will continue across the islands. A limited heat risk is expected through next week due to the combination of above-normal temperatures, southeasterly flow, and increasing humidity.

Long Term(Friday through Tuesday)

Issued at 317 AM AST Tue Apr 28 2026

By the end of the week, a moist and unstable weather pattern will persist across Puerto Rico and the U.S. Virgin Islands, accompanied by a troughing pattern aloft, light to moderate southeasterly winds, and above-normal moisture across the forecast area. Current guidance suggests that precipitable water values will remain in the 75th percentile for this time of year, around 1.80 to 2.00 inches. This will continue to support a pattern of showers across windward areas early in the day, followed by active afternoon convection across the interior, northern, and northwestern portions of Puerto Rico. In addition, 500 mb temperatures will remain between -7 and -8 degrees C (near normal but sufficient to support isolated thunderstorm development), particularly where the strongest activity develops during the afternoon on Friday. Accordingly, a limited flood threat will persist on Friday due to the high potential for ponding of water on roads and in poorly drained areas.

From Saturday into early next week, a gradual drying trend is anticipated, leading to improving weather conditions. Precipitable water values will decrease to near-normal levels (around 1.5 inches or less), while 250 mb heights increase and 500 mb temperatures warm as ridging builds aloft, bringing greater atmospheric stability. Although afternoon showers may still develop due to local effects, their coverage and intensity will be reduced. Any shower activity during this period should be brief and limited.

Lastly, warm conditions will persist throughout the period as indicated by temperature guidance at 925 mb which suggests values will remain above normal through at least next weekend. Also, an east to southeasterly wind flow will prevail supporting those conditions. Maximum surface temperatures will range from the upper 80s to low 90s across coastal and urban areas, and from the low to mid 80s in higher elevations. Combined with high humidity, heat indices are expected to exceed upper 90s to low 100s degrees F each day. As a result, a limited heat threat will remain in place for urban, coastal, and low-elevation areas. Residents and visitors are encouraged to stay hydrated and avoid prolonged sun exposure during peak heat hours.

AVIATION

(06Z TAFS) Issued at 317 AM AST Tue Apr 28 2026

Mainly VFR conds expected at all TAF sites. Light/variable to calm winds early in the morning, becoming SSE btw 8-12 kt after 28/14Z. SHRA/TSRA may develop over interior/western PR and affect TJSJ/TJBQ btw 27/17-23Z, causing brief MVFR/IFR conds. VCSH are possible over eastern PR/USVI terminals after 27/23Z.

MARINE

Issued at 317 AM AST Tue Apr 28 2026

A surface high pressure system over the central Atlantic will continue to weaken, while a surface low strengthens over the northwestern Atlantic over the next few days. This weakening pressure gradient will promote light to gentle southeasterly winds through at least midweek, becoming more easterly by the latter part of the week. A surface trough over east of Puerto Rico combined with an upper-level trough will bring showers and isolated thunderstorms across the local waters today. Pulses of small, long- period northeasterly swell will continue to spread across the Atlantic waters and local passages for the next few days, though seas should remain between 2 and 4 feet.

BEACH FORECAST

Issued at 317 AM AST Tue Apr 28 2026

Pulses of a small, long- period northeasterly swell will continue to spread across local waters and passages, with conditions expected to diminish by Thursday. Moderate risk of rip currents will prevail along the northern and eastern beaches of Puerto Rico and the U.S. Virgin Islands. Although the risk remains low to moderate, beachgoers must exercise caution as life-threatening rip currents are possible along beaches under moderate risk. In addition to rip currents, beachgoers should remain weather alert as afternoon showers and thunderstorms are expected near northern coastal areas of Puerto Rico, resulting in heavy rainfall, gusty winds, and lightning.

SJU WATCHES/WARNINGS/ADVISORIES

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