244 FXCA62 TJSJ 112048 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 448 PM AST Tue Mar 11 2025 .SYNOPSIS... Fair weather conditions and warmer temperatures will persist through tomorrow under southeasterly winds. A wet and unstable weather pattern is forecast by the end of the workweek into the weekend due to the arrival of upper-level troughs and a frontal boundary. A long-period northwesterly swell will spread across the Atlantic waters and local passages around Thursday, resulting in hazardous seas and life-threatening rip currents. Another swell is anticipated during the weekend into early next week maintaining marine and coastal conditions deteriorated. && .SHORT TERM...Tonight through Thursday... Stable weather conditions under clear to partly cloudy skies were seen across Puerto Rico (PR) and the US Virgin Islands (USVI) today. Some showers moved across the windward areas due to a moisture patch during the morning hours. Maximum temperatures reached the upper 80s to low 90s, with heat index values in the upper 90s. Occasional life-threatening rip currents developed along the north-facing beaches of northern USVI and Puerto Rico. Calm weather conditions will dominate overnight and Wednesday morning due to a mid-to-upper-level ridge and a drier air mass. However, an approaching frontal boundary will increase moisture as early as Wednesday afternoon into Thursday. Meanwhile, a mid to upper-level trough aloft will also increase atmospheric instability. Based on the expected weather pattern, we can expect the rain activity to slowly increase by passing showers across the windward sections during the early morning and afternoon, with afternoon convection developing across the interior and northwest quadrant due to the east-southeast wind flow. For Thursday, winds will become variable, gradually shifting from the south-southwest before transitioning to a north-northeasterly flow as the pre-frontal trough approaches the islands, pooling additional moisture. The potential for thunderstorms and flooding rains will increase due to these factors and the arrival of the trough aloft, too. Therefore, an unstable and wet pattern will likely evolve by the second part of this workweek due to the factors mentioned above, among others. Although minimum temperatures will drop into the low 70s along the coast and in the low 60s or even lower in the mountains overnight, maximum temperatures will again climb into the upper 80s or low 90s on Wednesday due to the weak east-southeast wind flow. The arrival of a long-period northwesterly swell will result in life- threatening rip currents from the beaches near Rincon northward to Fajardo and the northern beaches in Culebra and the US Virgin Islands from late Wednesday night into Thursday. .LONG TERM...Friday through Tuesday... .PREV DISCUSSION... /issued 402 AM AST Tue Mar 11 2025/ A short-wave trough will move quickly just north of the area on Friday, and the 500 MB temperatures are now expected to warm by a few degrees to around minus 6/5 degrees Celsius. However, a surface front, pushed by a building surface high pressure over the western Atlantic, is expected to move over or close to the islands and linger across the region over the weekend. The relatively colder mid-level temperatures, combined with above-normal precipitable water (PWAT) content of 1.50 to 1.70 inches, will promote a wetter pattern across Puerto Rico and the U.S. Virgin Islands in general during the first part of the long-term period, with increasing chances of isolated thunderstorm development. Consequently, there will be a limited to elevated risk of excessive rainfall, leading to urban and small stream flooding and potential landslides and rockfalls in vulnerable and steep terrain. In the U.S. Virgin Islands, the highest probability of precipitation (40% to 60%) will occur from late Friday through the weekend as shower activity increases due to the expected frontal passage. An upper-level ridge building from the western Caribbean and a developing TUTT-low northeast of the Leeward islands will promote a drying trend across the local area for Monday and Tuesday, with PWAT values dropping between 1.00-1.20 inches. Meanwhile, the surface high pressure over the western Atlantic will strengthen, and the low-level winds will increase between 20 and 25 knots across the Atlantic waters and the Anegada Passage, particularly on Monday. Therefore, breezy conditions and an advective weather pattern are expected, with passing showers moving at times across the windward areas of the islands and limited afternoon shower development over the SW quadrant of PR. && .AVIATION... (18Z TAFs) Expect VFR conditions today. The potential to observe SHRA/+SHRA will increase after 12/12z, spreading into the interior and northern PR after 12/15z. This activity will impact the terminals, possibly creating MVFR conditions. Winds will prevail from the E-ESE at 10-15kt with sea breeze variations until 11/23z, when we expect they to become calm to light and variable, returning from the E-ESE after 12/13z. && .MARINE... A surface high pressure over the eastern Atlantic and a surface low and associated front over the western Atlantic will maintain winds from the east-southeast. These winds will become lighter and from the south on Wednesday. By the end of the week, the potential for showers over the local waters will increase as the front moves closer to the area, and winds turn from the east to northeast. A long- period northwesterly swell will spread across the Atlantic waters and local passages around late Wednesday night or early Thursday, with another swell from the north-northeast by the end of the weekend, resulting in hazardous seas. && .BEACH FORECAST... There is a low risk of rip currents across the islands tonight and Wednesday. A 4 to 5 feet northwesterly swell will spread across the Atlantic waters on Thursday and Friday, increasing the potential for life-threatening rip currents. A larger swell (6 to 8 ft) is expected later during the weekend into early next week, potentially resulting in large breaking wave action along the north-facing beaches of the islands. High Surf Advisory conditions and life-threatening rip currents are likely, particularly on Sunday. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM/AVIATION...CAM/YZR LONG TERM...DS MARINE/BEACH FORECAST...ERG/YZR
Contact © 2024, WeatherPR.com