Hurricane Season runs from June 1-November 30
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066 FXCA62 TJSJ 062008 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 408 PM AST Mon May 6 2024 .SYNOPSIS...Abundant moisture and increasing instability from an approaching mid-to-upper-level trough will maintain a wet and unstable weather pattern during the next few days. Due to the soil saturation and the much above- normal streamflows along PR`s principal rivers, any period of moderate to heavy rains may result in sudden urban and small stream flooding to localized flash floods and mudslides near areas of steep terrain. Additionally, due to the high moisture content, above-normal heat indices surpassing 102 degrees Fahrenheit. && .SHORT TERM...Today through Wednesday... Doppler radar indicated showers developed early this morning over northeastern Puerto Rico. As the day progressed, shower development was gradually observed downwind from the local islands, and around 10 AM AST, convective development began over central Puerto Rico and downwind from El Yunque National Forest. By noon, shower activity intensified and spread across most Puerto Rico. So far, radar estimates recorded around 3 to 5 inches of rain in and around Coamo, Adjuntas, San German, Jayuya, and Morovis. During this time, various Flood Advisories and one Flash Flood Warning for Coamo were issued. High temperatures have been in the mid 80s to lower 80s across most coastal sites. Winds were generally easterly with sea breeze variations at 10-15 mph, but gusty of up to 20-25 mph near the shower and thunderstorm activity. The wet pattern will persist during the forecast period, with precipitable water values holding at above-normal moisture levels around 2.0 to 2.4 inches. While an eastward moving high pressure will maintain light to moderate east to east-northeast winds at 5-15 mph at lower levels, conditions aloft will remain favorable for deep convective development with a weak trade wind cap inversion and the passage of an upper-level trough Tuesday into Wednesday. This wet and unstable scenario will not only support an active weather pattern, but the expected slow-moving showers will likely support an elevated flooding risk. Since soils are saturated and river streamflows are running much above normal, any period of moderate to locally heavy rain could lead to dangerous flooding impacts, as well as sudden mudslides and landslides in areas of steep terrain. For tonight, prolonged showers and isolated thunderstorms following the afternoon convection will continue to affect mainland Puerto Rico through the evening hours. As the night progresses, the shower and isolated thunderstorm activity will shift to the local waters and coastal areas of northern and eastern Puerto Rico, Vieques, Culebra, and the U.S. Virgin Islands. With the proximity and then passage of an upper-level trough, weather conditions will likely deteriorate Tuesday into Wednesday. Based on the model guidance, an increase in shower and thunderstorm activity is expected throughout the period, with peak activity likely on Tuesday afternoon and around midnight on Wednesday, when mid-level temperatures will drop to around -8 degrees Celsius and precipitable water values will peak around 2.3-2.4 inches. For that reason, we encourage residents and visitors to remain weather-aware and informed about these potential hazards and to monitor the forecast for future updates. Temperature-wise, a warm trend will continue, with daytime high temperatures ranging between the upper 80s to lower 90s along the coastal/urban areas and in the upper 70s to low 80s along the higher terrains. Combined with above-than-normal moisture, heat indices may exceed 102 degrees Fahrenheit across coastal areas of Puerto Rico and the local islands, as well as other urban areas. .LONG TERM...Thursday through Monday FROM PREV DISCUSSION... /issued 402 AM AST Mon May 6 2024/ The mid to upper-level trough will continue moving away from the region on Thursday, leaving the islands in a less favorable position for organized convection. A mid to upper-level ridge will try to build over the Northeast Caribbean Friday into the weekend, which may further decrease local instability, potentially bringing relief from the current weather conditions. At the surface, GFS Total Precipitable Water guidance suggests values returning to the typical values for this time of year from Thursday onward. However, patches of increased moisture may arrive occasionally. Regardless of whether we observe a mixture of sunshine and clouds each day, strong afternoon convection could develop due to local effects and sea breeze variations each day. Additionally, due to the atypical high sea surface temperature, the advection of a cooler air mass across the warmer waters may result in frequent nighttime showers, reaching the windward sections each night. Temperature-wise, combining high moisture content with the typical upper 80s to low 90s maximum air temperatures will result in heat indices between 100-107 Fahrenheit or even higher, especially during the daily maximum heating, across the USVI and PR`s urban and coastal areas where no significant rain is observed. && .AVIATION... (18Z TAFS) The potential for VCTS and showers will continue across most sites, promoting MVFR to brief IFR conditions, especially across PR terminals through 06/23Z. VCTS/VCSH are likely across all sites through the rest of the period. E to NE surface winds at 10-15 kts, and then becoming lighter and more variable after 05/23Z && .MARINE... A surface high-pressure building across the Western Atlantic will push a surface trough further east away from the Northeast Caribbean, promoting light to moderate trade winds. From late Tuesday night onward, pulses of northeasterly swell will spread across the regional waters. Afternoon convection may result in strong thunderstorms across the coastal sections of northern and western PR each day. Increasing shower and thunderstorm activity is likely on Tuesday and Wednesday. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...OMS/RC/DSR LONG TERM....ICP AVIATION...RC/DSR PUBLIC...RC/RVT
