Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
954 FXCA62 TJSJ 131524 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 1124 AM AST Thu Jun 13 2024 .UPDATE...Showers have dissipated from land areas. The band of convection that moved through with scattered showers has maintained its continuity and lies mostly south of Puerto Rico. Streamers--lines of convection downstream from islands--have also formed west of Saint Croix, Saint Thomas and Vieques and these will likely bring showers where they return to land this morning and early afternoon. Better convection with isolated thunderstorms is still expected to form in western Puerto Rico this afternoon. The temperature in San Juan has already reached 90 degrees and may actually reach or exceed temperatures from yesterday. The heat advisory for Saint Croix was upgraded to a warning. A heat advisory was added to Saint Thomas. The same warnings and advisories continue elsewhere and are specified in the zone forecast and the newly issued NPW Weather Message. Saharan dust will enter the area on Saturday and haze has been added to the forecast from 22Z Saturday the 15th to 04Z Monday the 17th. && .AVIATION... (12Z) VFR conditions will continue across the area except for SHRA/TSRA dvlpg aft 13/17Z ovr wrn and interior PR till 13/23Z. Wind flow easterly 10-15 kt with gusts to 25 kt on the coasts in sea breezes. && .PREV DISCUSSION... /issued 451 AM AST Thu Jun 13 2024/ SYNOPSIS... Moisture from a past tropical wave and frontal remnants will reach sectors of north and east areas during the morning. Diurnal heating and available moisture will promote localized and short- lived showers and isolated thunderstorms in the afternoon for western Puerto Rico. Although the heating trend will decrease through Friday, Excessive Heat Warnings are still in effect today from 10 AM to 6 PM for most urban and low elevation areas of the metro area, north- central, northwestern, and western Puerto Rico. Heat Advisories are also in effect at those same times for the rest of the coastal areas of Puerto Rico, including Vieques and Culebra, and St. Croix. Southeasterly winds and saharan dust will promote a hot and hazy weekend. SHORT TERM...Today through Saturday... An upper level trough now extending across the northern Leeward Islands into the eastern Caribbean will drift eastwards today through Friday, while a mid to upper ridge is forecast to build and then linger across the region into the upcoming weekend. Surface high pressure extending southwards to just north of the region and an induced trough east of the Lesser Antilles will maintain a light to moderate east to northeast wind flow through Friday. Trailing low level moisture from a departed tropical wave and an old frontal boundary will continue to be steered across the local waters and reach portions of the north and east coastal area during the rest of the morning. This will result in potential for brief showers and possibly isolated thunderstorms with moderate to locally heavy rains in isolated areas. Thereafter, a mix of good sunshine and few clouds can be expected the rest of the day. However the intense heating throughout the day along with available pockets of moisture moisture will aid in the development of some showers and isolated thunderstorms later in the afternoon. This activity should be of short duration and prolonged periods of heavy rainfall is not anticipated. By late Friday and into the upcoming weekend, another surge of Saharan dust of moderare to high concentration is forecast to spread across the region while the local low level wind flow becomes more southeasterly with and even drier airmass expected through Saturday. By then with the southeasterly winds expect another round of hotter and hazy conditions due to the combination of suspended dust particulates and the mid to upper leve ridging, which will favor subsidence and compression of the warm air resulting in limited convective development across the islands. Daytime high temperatures will be in the low 90s especially along the north ans west coastal areas with maximum heat indices expected to be in the low 100s once again with excessive heat impacts probable particularly along the coastal and urban areas. LONG TERM...Sunday through Wednesday... Hot and hazy conditions will continue to start the long term period. Current model guidance suggests precipitable water (PWAT) at below normal to normal values to start the period, with only few patches of more humid air, from frontal remnants, moving through the islands. Southeasterly surface windflow is expected to persist on Sunday as a Surface high is present over the Atlantic. This will steer warmer tropical air towards the islands, promoting overall warm to hot conditions. Heat related products will likely be issued for the islands later on. 925 mb temperatures are forecast to be above normal to start the period. Model guidance suggests more easterly winds to start the workweek as the Atlantic surface high weakens. Saharan dust particles will continue to start the period as well, promoting hazy skies at least through Tuesday. Although model guidance suggest some moisture over the mid levels, a more notable increase is suggested by Wednesday. Most available moisture for the period will remain below 850 mb, however. A decrease in PWAT values is now forecast for Monday and most of Tuesday, with an increase by Tuesday night and Wednesday. High pressure aloft will start to weaken as we head into the workweek. AVIATION... (06Z TAFS) VFR at all TAF sites durg prd but VCSH at TJSJ and USVI terminals til 13/13Z. Mstly isold passing SHRA ovr regional waters en route btw islands. Aftn VCSH/Isold TsrA psbl ovr ctrl interior and west PR til 13/23Z...some may briefly impact areas in and around TJMZ/TJBQ. SFC wnd fm E-NE 10-15 knots with local sea breezes accompanied by higher gusts. Wnds bcmg less than 10 kts aft 13/23Z. Otherwise no significant operational wx impacts. MARINE... Surface high pressure over the Atlantic and an induced trough east of the area will promote light to moderate east to northeast winds through tomorrow. Frontal remnants from the northeast and an upper level trough are expected to increase the potential for showers and isolated thunderstorms through tomorrow. Winds will continue to diminish and veer, becoming east-southeast to southeast throughout the weekend. BEACH FORECAST... There is a moderate risk of rip currents today for easternmost St. Croix. For tonight, there is a moderate risk of rip currents for SE Puerto Rico. Low risk elsewhere today and tonight. For tomorrow, a low risk of rip currents is forecast for all beaches. Even with a low rip current risk, life-threatening rip currents often occur in the vicinity of groins, jetties, reefs, and piers. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Excessive Heat Warning until 6 PM AST this evening for PRZ001- 005-008-010. Heat Advisory until 6 PM AST this evening for PRZ002-003-007- 011>013. VI...Excessive Heat Warning until 6 PM AST this evening for VIZ002. Heat Advisory until 6 PM AST this evening for VIZ001. AM...None. && $$ SHORT TERM/MARINE/AVIATION...WS UPPER AIR/PUBLIC....ERG