textproduct: San Juan

KEY MESSAGES

Issued at 217 PM AST Mon Sep 28 2026

- Life-threatening rip currents continue along the north facing beaches of Puerto Rico, where a High Rip Current Risk remains in effect through late tonight.

- The heat risk for the next few days should be limited, as easterly trade winds strengthen, allowing only localized areas across Puerto Rico and the US Virgin Islands to experience short periods of near heat advisory criteria.

- Passing showers will continue to move at times across the USVI and eastern PR, while afternoon thunderstorms develop each day over western PR.

Short Term(This evening through Wednesday)

Issued at 217 PM AST Mon Sep 28 2026

Fair weather conditions have prevailed over the morning hours, with a few passing showers across the US Virgin Islands and eastern Puerto Rico leaving minimal accumulation and a light southeasterly wind flow. The rest of the day will be dominated by similar fair conditions. Seasonoal-to-below seasonal precipitable water (PWAT) values (below 2 inches) will persist through the day along with calm- to-locally breezy ESE wind flow. Drier mid-to-upper levels will act to hinder the development of showers and thunderstorms. However, mid- tropospheric temperatures are still conducive for development of convective cells. This pattern suggests that any weather that does develop will be driven by local effects. Thus, passing showers and streamers from El Yunque and the smaller islands may develop during the early afternoon hours over the US Virgin Islands and eastern Puerto Rico. Whereas, showers and thunderstorms may develop across the interior and western Puerto Rico through the afternoon hours. Where deep convection and excessive rainfall does occur, there might be ponding of water in roads and poorly drained areas, along with a low chance of small streams flooding.

A similar weather pattern is expected for the remainder of the short- term forecast with seasonal conditions driven by local effects. Thus, expect to see passing showers develop over the US Virgin Islands and Puerto Rico during the morning hours and showers and thunderstorms over the western interior and northwestern Puerto Rico during the afternoons. Out of all the days in the forecast, Tuesday promises to be the most active with above average PWAT values expected across western Puerto Rico during the afternoon. Tuesday is also forecasted to have a moister column, have locally breezy wind conditions, and low mid-tropospheric temperatures. These conditions are favorable for the development of showers and streamers from El Yunque and the smaller islands. Model guidance suggests that wind conditions are expected to further strengthen by Wednesday, bringing more widespread windy conditions to the CWA. They also indicate drier and warmer mid-levels which will act as a limiting factor for the development of rainfall activity. Nonetheless, showers and thunderstorms are still possible given the windy conditions and local effects.

The short-term period might provide some respite from the high temperatures that have been observed in the recent periods with lower low-tropospheric temperatures (around 925 mb) ranging around normal-to-below normal levels for the season. Thus, the heat risk for the remainder of the short-term period will remain limited. Heat risk will predominantly affect exposed and urban areas. While there is a decreasing trend in temperatures, citizens and visitors are still urged to remain updated of the changing weather conditions.

Long Term(Thursday through Monday)

Issued at 113 AM AST Mon Sep 28 2026

No major changes were introduced to the long-term forecast, with unstable conditions returning by the end of the week. As mentioned in the previous discussion, a surface high pressure building over the Western Atlantic should promote an easterly-southeasterly wind flow throughout most of the period. Breezy conditions are likely on Thursday, particularly across coastal areas of the islands, though winds may weaken by Friday as model guidance suggests a surface trough interacting with the surface high, strengthening back by Sunday. In the mid and upper levels, the interaction between the ridge over the Hispaniola and a TUTT over the Leeward Islands should bring more stable conditions as the CWA continues under the subsidence side of the trough on Thursday. Afternoon convection can still be expected, though showers should be progressive with short- lived thunderstorms. A transition to a seasonal weather pattern with unstable conditions is expected by Friday, with abundant tropical moisture pooled into the region and upper-level troughs near the area. As mentioned in the previous discussion, the deterministic guidance of the ECMWF and GFS suggests an increase in PWAT values most likely to range between 1.8 and 2.0, normal for this time of year. Taking a look at the cross-section, moisture content in the low to mid levels should increase to near above climatological normal (between 60 - 80%), with guidance suggesting skinny sounding profiles with weak inversion caps. In terms of instability, the presence of the trough should introduce cooler air in the mid levels (500 mb temperatures down to -7.5 C) and divergence aloft, favorable for deeper convection. This pattern should persist on Saturday as well, improving by Sunday as a drier airmass filters into the region and limits deep convection. Overall, afternoon convection is expected each day, particularly across interior and western/northwestern Puerto Rico, along with the local island streamers. Windward sections of the islands can expect isolated to scattered showers during the night and morning hours, though the eastern side of Puerto Rico could have additional rainfall due to streamers during the afternoon. Although the weather conditions do not seem optimal for flooding, ponding of water over roadways and poorly drained areas can be expected on Thursday. On the other hand, the flooding threat should increase on Friday and Saturday, with urban and small stream likely across the aforementioned areas, without ruling out the San Juan Metro Area. For the moment, the flooding threat should remain low on Sunday. In addition to flooding, thunderstorm activity could produce gusty winds and frequent lightning.

As mentioned in the previous discussion, seasonal to warmer conditions are still on forecast, with above climatological normal 925 mb temperatures during the second part of the workweek. Although afternoon convection may start earlier, temperatures may rise quickly during the morning hours, with heat indices exceeding 100 F across urban and low-lying areas. Therefore, the heat threat will remain limited to elevated throughout the forecast period.

AVIATION

(18Z TAFS) Issued at 217 PM AST Mon Sep 28 2026

Mainly VFR conditions are expected to prevail across all terminals during the next 24 hours. However, passing SHRA may cause tempo MVFR conds at TIST thru 28/21z. Elsewhere, mostly VCSH expected. The 28/12z TJSJ sounding indicated east winds up to 17 kt blo FL030. Light and variable winds expected overnight, increasing from the ENE at 12-16 kt with higher gusts aft 29/13z.

MARINE

Issued at 217 PM AST Mon Sep 28 2026

A small northerly swell will persist across the Atlantic waters and passages through tonight as moderate easterly trade winds gradually strengthen. Choppy conditions will continue across the Atlantic waters and Mona Passage, with locally fresh winds expected by Tuesday night into Wednesday. Periods of showers will remain possible across the local waters, with the more typical afternoon activity and isolated thunderstorms expected near western Puerto Rico. Thunderstorms may produce locally higher winds and seas, lightning, and reduced visibility at times.

BEACH FORECAST

Issued at 217 PM AST Mon Sep 28 2026

A northerly swell will maintain a high rip current risk through at least late tonight from northwestern through northeastern Puerto Rico, including the San Juan metro area, where life-threatening rip currents are expected. Therefore, a Rip Current Statement is in effect for those areas, and beachgoers are urged to avoid those beaches as dangerous rip currents are expected. Moderate rip current risk continue in the western beaches of Puerto Rico, as well as Vieques, Culebra and the U.S. Virgin Islands.

The moderate risk will continue along the northern, eastern and western beaches, including Vieques, Culebra and the U.S. Virgin Islands due to strengthening easterly trade winds. This means that rip currents are possible in the surf zone.

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk through late tonight for PRZ001-002-005- 008.

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