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FXCA62 TJSJ 260817 AFDSJU

Area Forecast Discussion National Weather Service San Juan PR 417 AM AST Fri Apr 26 2024

SYNOPSIS

Another active day is expected across the local area due to an approaching mid-to-upper-level trough. Above-normal moisture in combination with daytime heating and local effects will enhance the potential for heavy showers and thunderstorms, mainly across the central interior and western Puerto Rico. There is a limited to elevated risks of flash flooding, urban and river flooding, and landslides for the mentioned areas. We encourage citizens to stay informed and monitor our forecast for additional updates.

SHORT TERM
Today through Sunday...

Puerto Rico and the U.S. Virgin Islands experienced calm weather conditions, with a mid-to-upper-level cloud layer moving across them. Our Doppler Radar detected most rain over the waters, with some moving mainly across southeast Puerto Rico. Low temperatures across the coastal areas ranged around the mid-70s and in mountains and valleys around the mid-60s. The prevailing winds are now more from the east, though land breeze fluctuations developed overnight.  

We anticipated an increase in low-level moisture as the front/shear- line moves near PR and eventually the USVI. The latest model guidance suggests an increasing instability trend due to an approaching mid-to-upper-level trough accompanied by a jet stream.
This weather pattern could lead to deep convective activity, particularly during the afternoons, when diurnal heating, local topography, and sea breeze may play an additional role, enhancing the convection. We strongly encourage citizens to stay informed and monitor our forecast for further updates, which will empower you to plan and prepare effectively.

Today, we expect calm weather in the morning, with an increase in showers and thunderstorms by early this afternoon. The strongest thunderstorms are possible across the western interior and western PR. Showers will then increase across the Virgin Islands by late this afternoon into the evening and early Saturday morning as a plume of moisture kicks in, resulting in showery weather, with possible isolated thunderstorms moving inland from the surrounding waters. Eastern PR may observe unsettled weather conditions from early Saturday morning to afternoon. Winds will shift from the NE, shifting the focus of strong afternoon convection across the southwest quadrant and southern slopes of PR, while moisture may erode over the Virgin Islands by Saturday afternoon. For that reason, the risk of flooding remains elevated across most islands, especially during the afternoons today and Saturday. It's crucial to be cautious and aware of these potential risks.

We expect a solid surface high pressure moving off the eastern coast of the USA, promoting breezy northeast winds across the Northeast Caribbean around Sunday. This wind flow introduces some discrepancies in our model guidance regarding the final position of the plume of moisture. Therefore, our model guidance has moderate to high uncertainty about how much moisture may pool over the islands on Sunday if it remains over them or further south across the Caribbean Sea. Regardless of the discrepancies, unstable and possibly showery weather remains possible that day.

LONG TERM
Monday through Friday...

A strong surface high pressure located over the eastern coast of the United States will promote a northeasterly wind flow from Monday through Wednesday. As this feature moves from the western to the central Atlantic winds are expected to veer from a more easterly component through the rest of the long-term period. Previous model runs indicated a drying trend for the beginning of the workweek, however, the latest model guidance now suggests a prolongation of above-normal moisture across the islands. The precipitable water content values are between 1.60 to 1.80 until Wednesday, then increasing up to 2.20 inches through the rest of the period. A vast moisture field coming from South America to the eastern Caribbean will help to enhance the shower and thunderstorm activity across the islands. This wet and unstable weather pattern will promote rainfall activity everyday across the area, especially over portions along the Central Cordillera, eastern, and western portions of Puerto Rico. The U.S. Virgin Islands will also experience moderate to locally heavy showers by the end of the period. With the expected weather scenario limited to elevated risks of urban and river flooding, flash flooding, and landslides will continue to impact areas already saturated by the previous days/week rainfall activity.
Daytime temperatures are expected to stay in the mid 80s along the coastal and urban areas of Puerto Rico and the U.S. Virgin Islands, and from the upper 70s to low 80s across the interior.

AVIATION
(06Z TAFs)

Mainly VFR conditions expected to prevail across all terminals.
However, SHRA/TSRA expected to develop over the western interior may lead to mtn tops obscd and MVFR cigs in and around TJBQ/TJPS btw 26/18z-22z. Also, after 26/23z showers en route from the Leeward Islands/Atlc waters may cause brief -SHRA or MVFR conds at TISX/TIST/TJSJ thru the rest of the overnight hours. East winds up to 12 kt with sea breeze variations aft 26/14z, bcmg ENE around 26/21z across most terminals.

MARINE

A small northwesterly swell will continue to spread across the local waters through today. Showers and thunderstorms will continue to affect the local waters for the next several days as lingering moisture from a surface trough/old frontal boundary remains over the local area. Winds will prevail from the east and becoming northeast on Saturday under the influence of a surface high pressure moving off the eastern coast of the United States.

BEACH FORECAST

Breaking waves of around 5 feet will maintain the risk of rip currents moderate for the northern beaches of the local islands.

SJU WATCHES/WARNINGS/ADVISORIES
PR...None.
VI...None.
AM...None.

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