Hurricane Season runs from June 1-November 30
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000 FXCA62 TJSJ 250912 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 512 AM AST Thu Apr 25 2024 .SYNOPSIS... Wet and unstable weather conditions are expected to prevail for the next few days with limited to elevated risks of flash flooding, urban and river flooding, and landslides mainly over the interior, western, and northern Puerto Rico, as well as the San Juan metro area. A slight improvement on weather condtions is expected by Saturday night into Sunday as drier air filters into the local area. && .SHORT TERM...Today through Saturday... Isolated to scattered showers affected the eastern third of Puerto Rico and smaller islands during the night hours. However, most of the activity remained over the Caribbean waters. Radar estimates indicated up to 0.60 inches of rainfall fell mainly over and near El Yunque. Similar activity is expected for the rest of the morning hours over windward coastal areas. According to the Tropical Analysis and Forecast Branch (TAFB) surface analysis, the axis of the surface trough that has been over the CWA for the past few days will finally move northwestward today. However, plenty of columnar moisture, combined with diurnal heating and local effects, along with marginal instability aloft, will promote another active afternoon. Model guidance suggests that the bulk of the activity will be clustered a bit further north than the previous day steered by southeast to east-southeast winds. Nonetheless, heavy showers and thunderstorm activity will generally be observed in already saturated soils and areas with elevated streamflows. While the overall wet and unsettled weather pattern will persist for the remainder of the short-term forecast, some changes have been suggested by the latest model cycle for Friday and Saturday. Late tonight through early Friday, we could observe a slight decrease in showers, mostly across the eastern CWA, as a slot of slightly drier air moves in. However, this respite won`t last long as the pre- frontal trough currently affecting the Dominican Republic will gradually move over the local area by Friday, increasing low-level instability and moisture convergence over the region. Meanwhile, a mid-level short-wave trough will strengthen and pass over the northeastern Caribbean, further enhancing the potential for deep convective activity. Therefore, another afternoon with widespread activity is expected on Friday. By Saturday, previous model cycles indicated a drying trend, which was expected to limit the areal coverage of convective activity across the area. However, the latest model cycle now suggests a prolongation of above-normal moisture across the islands. The GFS Galvez Davison Index suggests the potential for isolated to scattered thunderstorms and heavy rainfall on Saturday afternoon, delaying the transition to a more stable weather pattern. Additionally, cold air advection at mid-levels will be high, with 500 mb temperatures falling between -8 and -9 degrees Celsius. This will enhance low- to mid-level lapse rates and increase the potential for strong thunderstorms capable of producing frequent lightning and gusty wind conditions. Overall, expect a wet and unstable weather pattern throughout the short-term forecast, with limited to elevated risks of flooding and lightning across the area, particularly over interior, western, and northern Puerto Rico, as well as the San Juan metro area. Urban and river flooding, flash flooding, and landslides will continue to impact areas already affected in the past week. Please continue to monitor the forecast in the next few days and pay attention to any advisories or warnings that our office may issue. .LONG TERM...Sunday through Thursday... A strong surface high pressure moving off the eastern coast of the united states, is expected to promote moderate to locally fresh northeast winds at the beginning of the long-term period. The latest model guidance have changed, delaying the departure of the moisture from the local area. However, by Sunday remnant moisture from a surface trough and old frontal boundary will be pushed south of the region, improving gradually the local weather. Variable weather conditions are expected from Sunday through Tuesday, with passing showers over the east coast of Puerto Rico and the U.S. Vrigin Islands. Then, followed by afternoon convection across the southwest portions of PR due to the combination of daytime heating and local effects. Precipitable water values will remain between 1.40 to 1.50 inches through Tuesday night. By Wednesday, a patch of very dry air will filter into the region, limiting the potential of shower activity across the islands. However, this fair weather pattern will not last long due to the arrival of a big field of moisture pulled from South America toward the eastern Caribbean region on early Thursday. A wet and unsettled pattern is anticipated with an elevated potential of showers and thunderstorms across the local area. The general wind flow will be from the northeast then veering from the east southeast by Thursday. Daytime temperatures will remain in the mid 80s along the coastal and urban areas of Puerto Rico and the U.S. Virgin Islands, and from the mid to upper 70s across the Cordillera Central. && .AVIATION... (06Z TAFs) Expc mainly VFR conditions across all terminals through the forecast period. However, areas of SHRA and SCT TSRA this aftn could produce tempo MVFR/IFR conds and mtn obsc, particularly ovr TJBQ/TJSJ aft 25/17z. VCTS/SHRA at TJPS for the most part. ESE winds reaching speeds of up to 8-12 knots, accompanied by higher gusts and sea breeze variations aft 25/13z. && .MARINE... A small northwesterly swell is expected to spread across the local waters today. Showers and thunderstorms will continue to affect the local waters for the next few days. Another surface trough will strengthen the easterly winds from today into Friday, before 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 3 feet will maintain the risk of rip currents generally moderate for the northern beaches of the local islands. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...CVB LONG TERM....GRS
