Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
492 FXCA62 TJSJ 240839 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 439 AM AST Mon Jun 24 2024 .SYNOPSIS... The arrival of a tropical wave today will bring showers and thunderstorms across the area, especially during the afternoon. A thick plume of Saharan dust will bring hot and hazy conditions from tomorrow through Thursday morning, then a trade wind pattern with advection showers and afternoon convection will prevail. Hot temperatures are expected through the week with a Heat Advisory in effect for northern and western Puerto Rico and a watch for tomorrow afternoon for all the coastal sections of PR and the USVI. && .SHORT TERM...Today through Wednesday... Passing showers have been moving across Puerto Rico and the United States Virgin Islands during the night hours. The strongest activity was observed early in the night, across northeastern Puerto Rico, with lightning detected. All this rain is related to a tropical wave near the Lesser Antilles. The field moisture is evident in the satellite-derived precipitable water product. As the wave progresses today, moisture value will remain well above the climatological value for this time of year, meaning that conditions will be favorable for showers and thunderstorms. It will be gusty too, with a southeast breeze at 15 to 25 mph. The risk for flooding will be elevated, with lightning and gusty winds anticipated with the thunderstorms. Once the wave departs, a dense Saharan Air Layer follows, so conditions will dry out later this evening. Hazy skies and hot temperatures are anticipated for Tuesday and Wednesday, with only a few showers reaching the islands at times. Afternoon convection will remain possible for western Puerto Rico, but conditions aloft will not favor widespread nor strong rainfall accumulation. && .LONG TERM...Thursday through Monday... Through early in the weekend, there will be a mid-to upper-level ridge across the northeastern Caribbean. Its still possible that afternoon showers will form across the western sections of Puerto Rico. Instability will slightly increase from late Thursday and Friday as an induced low-level trade wind perturbation streams across the local area raising moisture content that will increase the chance of isolated thunderstorms and showers. A trade wind pattern due to an established surface high across the Atlantic basin will drag tropical moisture into the islands through the weekend into next week. According to global model guidance, PWAT values will fluctuate from 1.70 to 2.10 inches, just above seasonal climatological values for the region. That moisture, along with diurnal heating, will promote the development of afternoon showers and isolated thunderstorms each day across the western interior sections of Puerto Rico. The arrival of drier air on Monday may reduce the chance of showers, however do still expect a typical seasonal pattern of passing showers and afternoon convection for the start of the following week. && .AVIATION... (06Z TAFs) SHRA and isolated TSRA from a tropical wave will move across the area today, reaching the terminals at times. The activity will be strongest after 15Z, with periods of reduced VIS and low ceilings expected. Winds will be from the southeast from the surface through FL150, at 14-24 kts. && .MARINE... A surface high pressure over the central Atlantic will promote light to moderate southeasterly winds. Trade wind showers will move across the regional waters from time to time. The next tropical wave will approach the local islands from late tonight through Monday. Increasing winds and showers with thunderstorms are expected through tonight across the local waters. Hazy skies are expected from Tuesday through Thursday due to Saharan dust. && BEACH FORECAST... There is a low to moderate risk of rip currents across PR and the USVI. Showers and isolated thunderstorms are possible across the coastal areas of the USVI and eastern PR during the morning hours, and across the west/northwest coast of PR during the afternoon. The afternoon thunderstorms could produce frequent lightning and gusty winds. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Heat Advisory from 10 AM this morning to 2 PM AST this afternoon for PRZ001-005-008-010-011. Excessive Heat Watch from Tuesday morning through Tuesday afternoon for PRZ001>003-005-007-008-010-011. VI...Excessive Heat Watch from Tuesday morning through Tuesday afternoon for VIZ001-002. AM...None. && $$ SHORT TERM...ERG LONG TERM....RC