Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
473 FXHW60 PHFO 201937 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 937 AM HST Fri Sep 20 2024 .SYNOPSIS... A moderate to locally breezy trade wind pattern will continue through this evening. Shower activity is expected to increase this weekend as a weak disturbance moves through the Hawaii region. A drier and more stable trade wind pattern will return early next week. && .DISCUSSION... Satellite and radar imagery show low clouds and scattered showers moving into windward areas on the trades this morning, with a few showers circumnavigating or passing over some of the island terrain into leeward areas at times. High clouds can also be seen moving across the region from the west. Temperature inversion heights around 9000 feet as measured at Hilo around 2 AM this morning are allowing for brief moderate downpours. A moderate to breezy trade wind pattern will continue today, with shower activity expected to decline later this morning into the afternoon. While seasonal temperatures are expected again today, if the high clouds thicken up persist through the day temperatures might be slightly lower than average this afternoon, but model simulated satellite imagery shows that these high clouds should gradually decrease in coverage through the day. A shift in the pattern is expected this weekend as the trades weaken on Saturday in response to a weak low level trough approaching from the northeast, an upper level low dips down over the state from the north Saturday night into Sunday, and another weak low level trough moves in from the west. With modest forcing in both the low to mid levels and pockets of low level moisture in the trades, trade wind showers will likely be enhanced this weekend, especially Saturday night into Sunday. In addition, cooler temperatures aloft will move overhead with the mid to upper level low, allowing instability to increase...which raises the question of whether or not we`ll see any thunderstorms this weekend. With only marginal instability, small pockets of low level moisture, and weak surface forcing, decided to hold to the previous forecast philosophy and keep any mention of thunder out of the gridded forecast through the weekend. A drier and more stable moderate trade wind pattern will return early next week as the upper level low and surface trough both move west of the state. Brief overnight to early morning showers will be possible over mainly windward and mountain areas. && .AVIATION... Moderate to locally breezy trade winds will carry pockets of moisture, leading to periods of MVFR conditions along windward slopes through the next 24 hours. AIRMET Sierra for mountain obscuration has been dropped for windward Big Island, Maui, and Molokai, but these conditions may redevelop over some islands overnight. VFR will prevail over leeward areas. An upper-level low will move over the state during the weekend and could bring a more active shower pattern with higher chances for MVFR conditions over windward and mauka areas by Saturday night. && .MARINE... Fresh to strong easterly trade winds will continue through Saturday, then ease into the gentle to moderate range Sunday through Monday as a weakness forms in the ridge to the north. A Small Craft Advisory (SCA) remains in effect for the windier waters around Maui County and the Big Island through early Saturday. This may need to be extended through the day Saturday, before being lowered as the winds begin to trend down during the latter half of the weekend. Surf along north facing shores will trend up through the first week of fall, beginning next Tuesday in response to a gale developing near the Kurils today, racing eastward across the Date Line near the Aleutians this weekend, then to the Gulf of Alaska early next week. Guidance shows this northwest swell peaking locally Tuesday night into Wednesday out of the northwest, then fading Thursday into Friday as it shifts out of a more north- northwest direction. Surf along east facing shores will remain small and choppy into Saturday, then decrease Sunday into next week as the trades lower locally and upstream across the eastern Pacific. Surf along south facing shores will remain small through the weekend, with mainly a mix of background long-period southwest and short-period southeast swells moving through. An upward trend is possible Tuesday through midweek due to a slightly larger southwest swell arriving. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Farris AVIATION...Wroe MARINE...Kino