Area Forecast Discussion

KEY MESSAGES

Updated at 134 PM AST Tue Apr 21 2026

* Afternoon showers with a few thunderstorms will develop across the interior and western PR each day; meanwhile, the USVI can expect calm weather with a few showers embedded in the winds. * Beachgoers can expect a moderate risk of rip currents along north- and east-facing beaches throughout the forecast period in PR and the USVI. However, a long period northerly swell will promote a moderate/high risk on Wednesday as this swell moves across the local Atlantic Waters.

* A wetter and more unstable weather pattern will set up over the region as early as Thursday afternoon and more likely from Friday into early next week.

Short Term(This evening through Thursday)

Issued at 134 PM AST Tue Apr 21 2026

In general, we observed calm weather across the USVI and PR in the morning. However, we detected a few showers moving inland across the USVI and the eastern third of PR at times. The rest of the islands had mostly clear skies with no rain. The winds were mainly from the east-southeast at 10 to 20 mph, with sea-breeze variations. Maximum temperatures were in the mid- to upper 80s.

This afternoon, showers and a few thunderstorms are expected to develop across the interior and western Puerto Rico due to local effects, sea breeze interactions, and diurnal heating. As a result, the risk of flooding in these areas is limited. Across the U.S. Virgin Islands, generally calm conditions are expected, with increasing cloudiness due to low-level advection. Occasional showers cannot be ruled out tonight and overnight.

A relatively drier air mass will move in tonight and persist through at least Thursday morning. By Thursday afternoon onward, an approaching frontal boundary will promote moisture pooling across the region, increasing shower activity. In terms of atmospheric stability, the region remains under relatively stable conditions, driven by zonal flow aloft and a weak mid-level ridge. These features will begin to erode by Thursday afternoon as a mid- to upper-level trough amplifies over the western Caribbean, becoming more pronounced from late Thursday night into Friday. At the surface, high pressure over the central and eastern Atlantic, interacting with a frontal boundary over the western Atlantic, will maintain an east-to-east-southeast wind flow through today, shifting to east-to-east-northeast on Wednesday and Thursday.

Under this pattern, a typical seasonal weather regime is expected. Wednesday will feature generally fair weather with passing showers across windward areas of Puerto Rico and the U.S. Virgin Islands, followed by afternoon convection over the interior and western Puerto Rico and downwind of the USVI. Additionally, residents can expect pleasant overnight temperatures, as mostly clear skies promote radiational cooling.

Long Term(Friday through next Monday)

Issued at 134 PM AST Tue Apr 21 2026

A wetter and more unstable weather pattern is expected to prevail at the start of the long-term period as remnants of a frontal boundary linger near the region under southeasterly low-level flow. This pattern will promote precipitable water values near or above climatological normals. Afternoon convective development will remain possible across interior and western/northwestern Puerto Rico, aided by daytime heating, local effects, and sea breeze convergence. While widespread rainfall is not anticipated on Friday, moderate rainfall may still cause localized ponding of water in urban and poorly drained areas, especially where showers persist or repeatedly affect the same locations.

Through the weekend, low-level winds are forecast to veer more southerly, allowing a deeper tropical moisture plume to spread across the area while also advecting warmer temperatures into the region. This evolving pattern will likely result in above-normal daytime temperatures, particularly across coastal and urban areas of Puerto Rico and the U.S. Virgin Islands. As a result, increased heat risk is possible during the peak hours of the day, with heat indices near or slightly above 100 degrees possible in some locations. Residents and visitors should anticipate warmer and more humid conditions through the weekend period.

Shower and thunderstorm coverage during the weekend will depend in part on the availability of mid-level moisture, as the latest guidance suggests some pockets of drier air aloft may intermittently limit the overall extent of convection. Nevertheless, sea breeze convergence, local effects, and stronger daytime heating may still support isolated to scattered afternoon showers and thunderstorms each day, with the greatest activity focused over interior and northern portions of Puerto Rico. Localized urban and small stream flooding will remain possible where stronger showers develop, along with brief gusty winds and frequent lightning.

By early next week, a gradual increase in columnar moisture in combination with some troughiness aloft is expected to support greater areal coverage of showers and thunderstorms across the forecast area. This should result in more numerous showers from Monday into Tuesday, with the greatest afternoon activity once again focused over interior and western/northwestern portions of Puerto Rico, while passing showers remain possible elsewhere. In this pattern, periods of locally heavy rainfall and isolated thunderstorms will be possible, increasing the potential for urban flooding, quick river rises, and localized flooding in flood-prone areas through the latter part of the forecast period.

AVIATION

(18Z TAFS) Issued at 134 PM AST Tue Apr 21 2026

Mainly VFR conds across all TAF sites with VCSH expect over USVI terminals and JPS through 21/23z. Aftn convc may bring -TSRA over W PR, with VCTS in JBQ btwn 21/18 - 21/23z. The proximity of the -TSRA may reduce CIGs/VIS and bring -RA, AMDs will be issued if required. Winds will weaken aft 21/23z, btwn 5 - 8 kt, while winds will strengthen btwn 10 - 12 kt, by 22/12 - 22/13z.

MARINE

Issued at 134 PM AST Tue Apr 21 2026

A high-pressure system extending from the central to the eastern Atlantic is interacting with a frontal boundary approaching from the western Atlantic. This setup will lead to moderate east-to- east-southeast winds tonight, followed by the return of the trade winds starting Wednesday. Additionally, long-period swells will move across the local Atlantic and Caribbean Passages. The first swell, arriving from the northwest, is expected to arrive around Wednesday afternoon, followed by a second, larger swell coming from the north to northeast around Saturday.

BEACH FORECAST

Issued at 134 PM AST Tue Apr 21 2026

Beachgoers can expect a moderate risk of rip currents through much of the forecast period, especially along north- and east- facing beaches of Puerto Rico and the U.S. Virgin Islands. Looking ahead, another long-period northerly swell will arrive around Wednesday afternoon, which could increase the risk to high, potentially worsening beach conditions.

In addition, beachgoers should remain alert for afternoon thunderstorms, particularly across western Puerto Rico. These storms may produce gusty winds and frequent lightning.

SJU WATCHES / WARNINGS / ADVISORIES

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