Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
469 FXHW60 PHFO 010643 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 843 PM HST Fri May 31 2024 .SYNOPSIS... Breezy to locally windy trade winds will continue through the weekend due to high pressure to the far northeast, with showers favoring the typical windward and mauka areas. These showers will be enhanced some due to an upper level trough moving over the islands. Expect winds and showers to diminish some as we head into the middle of the new week. && .DISCUSSION... A weakening surface trough to the west of the area is expected to dissipate over the next 24 hours. A high pressure to the far northeast will continue to support breezy to locally windy trades into the new week. The high is expected to slowly sink southward through the weekend, with little change in the pressure gradient over the islands. Meanwhile, a mid to upper level trough developing near and to the northeast of the islands will help to enhance trade wind showers. These showers are expected to favor the typical windward and mauka areas, but a few stray showers could reach leeward areas at times. There is good agreement in the ECMWF and GFS that the upper level trough will lift northward Monday/Tuesday and then move to the east Wednesday. During the same time, the high pressure system will weaken and be replaced by a new high. During this transition time we can expect trade winds to weaken some, and showers to diminish. The latest National Blend of Model run indicates a drier airmass that is currently in the forecast. Anticipate trending more to this with the morning forecast package. During the second half of the week, the new high lifts to the north, causing winds over the islands to weaken and become more southeasterly. This will likely mean more showers developing over the interior of the islands, primarily during the afternoon hours. Anticipate making some changes to the forecast PoPs during the end of the new week with the morning forecast package after taking a closer look at the model runs overnight. && .AVIATION... Breezy to strong trades are expected to increase slightly this weekend, as a surface high moves closer to the state from the northeast. Low cigs and SHRA will favor windward and mauka areas. MVFR conds in SHRA are possible with VFR conds prevailing elsewhere. AIRMET Sierra may be needed for mtn obsc later tonight as SHRA activity increases. AIRMET Tango is in effect for moderate low-level turb south through west of terrain as well as for moderate turb between FL300-FL400. && .MARINE... A 1030 mb surface high centered 1000 nm NE of the islands will change little as it sags slowly S later this weekend, resulting in fresh to strong ENE trade winds across the area. This trades will prevail into early next week, as the surface high remains nearly stationary. A Small Craft Advisory (SCA) continues through at least tomorrow afternoon for most zones. This product may have to be extended through Sunday as strong trades remain intact. Long-range guidance indicates a trend toward diminishing and veering winds around the middle of next week as the ridge to the N is weakened by a passing front. There will be an extended run of elevated surf along S facing shores over the next week (and likely longer), with the largest of the swells likely to produce surf near High Surf Advisory (HSA) levels of 10 feet. The first of several pulses of long- period SSW swell will gradually build tonight, and peak near HSA heights later Saturday into Sunday. Latest buoy observations indicate some modest energy increases in the longer periods, resulting in inconsistent and small sets at the moment. Additional pulses of swell arriving early next week will persist through the middle of the week, with the potential for a larger swell by the following weekend. A strong, slow-moving low in the distant NW Pacific has generated a small NW swell that will arrive Monday and Tuesday, with the potential for a small follow-up NW swell generated by the extra- tropical version of former west Pacific Typhoon Ewiniar. Trade winds will continue to generate short-period wind waves that will support choppy surf along exposed E facing shores. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Saturday for Kauai Northwest Waters-Kauai Leeward Waters-Kauai Channel-Oahu Windward Waters- Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters- Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...M Ballard AVIATION...Walsh MARINE...Thomas