267 FXHW60 PHFO 241342 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 342 AM HST Fri May 24 2019 .SYNOPSIS... Trade winds are expected to return this afternoon and continue through at least the first half of next week as a ridge of high pressure stays north of the islands. With the return of the trades, we can expect showers to favor the windward and mountain areas, especially during nights and mornings. Lee areas will continue mainly dry. && .DISCUSSION... The islands are at the western end of a large and broad area of high pressure centered far northeast of the islands. A ridge extends southwestward from the high to roughly 240 miles north of Kauai. This close proximity of the ridge to Kauai has kept an east- southeast wind flow across the main Hawaiian Islands for a couple of days. The ridge is also held in place by a front to the west of the islands. This front, about 340 miles west- northwest of Kauai at 3 am HST, is moving eastward but should be stalling later this morning at a distance of 250 miles northwest of Kauai. The stalled front will then slowly weaken through the first half of the new week. As the front stalls, the ridge will start to head north, allowing trades to spread across the main Hawaiian Islands. In doing so, a surge of locally strong trades are expected for the waters around the Big Island lasting from tonight to through Saturday. The trades will then ease slightly to moderate speeds that will last through Wednesday of next week. Models are hinting of a slight change in wind direction Monday evening through Tuesday for the western islands, where the winds acquire a slight south component, or east- southeast once more. If this outlook holds, we may see lighter winds for Oahu, Kauai, and Lanai on Monday, leading to local sea breezes, and ending in some afternoon clouds and a few showers over lee and interior areas of all islands. The islands are and will remain under a rather stable air mass through this weekend, at between 7 and 9k feet. Models are now saying the ridge aloft weakens, allowing the inversion to rise to 10 to 13k feet over the Big Island on Monday, and 8 to 10k feet elsewhere. So, we could be encountering some heftier showers between Monday and Tuesday of next week. Inversion levels off at between 7 and 10k feet over the Big Island on Wednesday, as well as elsewhere. Trades are expected strengthen after Tuesday night, to locally strong, that will last into next weekend. The north to south oriented band of showers is now starting to affecting Maui County, with the core of the band just about to move onto windward Maui. Oahu is up next, with increasing clouds and showers shortly after sunrise. These clouds and scattered showers could linger across Oahu all day today, if not most of today. The back edge of the band is about to reach Cape Kumukahi of the Big Island. So windward Big Island is poised to get some partly clearing this morning. There is more shower bearing clouds upwind of the Big Island, however, that may impact the windward sector later today. Models, though, are saying that most of these clouds would dissipate as the morning progresses, and we are banking on this to happen. && .AVIATION... TAF sites are VFR and should remain so through tonight. However, a band of clouds and showers is moving through the chain, impacting Maui and the Big Island. AIRMET Sierra for mountain obscuration is in effect for north and east sections of the Big Island. No other AIRMETS are in effect at this time. Winds are forecast to increase slightly and shift more out of the east today, so clouds and any showers will likely favor the typical windward coasts and slopes with less cloud cover over leeward areas in the afternoon. The Kona coast of the Big Island will remain wind- sheltered, so afternoon clouds are expected there once again. && .MARINE... A surface ridge north of Kauai will drift south over the next day or so as a front, now sitting far northwest of the state, stalls on the edge of the offshore waters. As a result, easterly trade winds around the Big Island and Maui County will be in the breezy to low-end strong range, putting those waters under border- line Small Craft Advisory (SCA) conditions. Due to the proximity of the front and blocking from the upwind islands, winds shift out of the east-southeast and weaken near Oahu and Kauai. As the front dissipates later today and Saturday, the ridge north of the islands will exert a greater influence, and easterly trade winds will surge back across the entire island chain. Expect moderate to breezy trades to then dominate across most waters into next week, with periods of SCA conditions possible for the typically windy waters around the Big Island and Maui. Near to above seasonable average surf is due along south facing shores through the holiday weekend, while north facing shores see a brief pulse above seasonable average. The current south- southwest swell will produce surf mainly in the head high range through today. As this swell declines Saturday, forerunners from a larger south-southwest swell will fill in, and south shore surf will peak around the 8-foot advisory level Sunday and Memorial Day. Surf will drop to near seasonable average during the middle of next week. A pulse of relatively short period northwest swell will arrive late today and peak Saturday and early Sunday, producing surf a few feet over seasonable average though well below the north shore advisory level. This swell should drop a notch on Memorial Day, with surf holding around seasonable average through the middle of next week. Along east facing shores, trade wind swell will pick up to around seasonable average (6 ft 8 seconds) late today or Saturday, hold through Sunday, then drop slightly next week. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ Lau/Powell/Kinel