Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
312 FXHW60 PHFO 031337 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 337 AM HST Wed Jul 3 2024 .SYNOPSIS... The recent stagnant, relatively dry pattern under weakened trade flow will persist through the holiday weekend. Surface high pressure far northeast of the islands will weaken in response to eastern Pacific troughing. This will maintain light to gentle east trade winds through the week. Upper level ridging over the islands, along with easterly dry air, will ensure continued mainly clear to partly cloudy skies, warmer conditions with little to no statewide rainfall. Shower behavior that produces any measurable rainfall will generally focus along windward slopes primarily during the nocturnal hours. && .DISCUSSION... The overall Hawaiian Island weather pattern will be controlled by upper level ridging and a pair of quasi-stationary surface high pressure cells thousands of miles north and northeast of the state. The general early month synoptic set up will evolve with the northeast high moving further away as troughing develops between us and the high. This, in tandem with the other high cell north of the islands drifting further west, will weaken the downstream pressure gradient enough to generally hold light to gentle east trades in play through the Independence Day holiday weekend. Upper to mid level ridging will remain over the central Pacific and provide ample subsidence. This, along with a large dry air mass moving around the base of eastern Pacific troughing and advecting in across the area through late week, will provide the main ingredients for continued dry and warm weather. If NWP guidance holds true with the characteristics of this unseasonably dry air mass, it will fall within the lower 10th percentile for this time of year (near 0.9 inch pwats compared to early July climatology norm 1.3 inch pwats). The added subsidence will create more clear, island-wide sunny skies. This will ultimately result in warmer afternoon temperatures. Trades will introduce thicker clouds and occasional typographically-enhanced low rainfall accumulation showers over windward (mauka) zones during the overnight and early morning hours. Leeward areas should remain mostly to partly sunny with that rare light shower making its way over the ridgeline. The lone exception to this rule will be those warmth-of-the-day afternoon clouds/weak showers that will inevitably form along leeward Haleakala and Big Island. && .AVIATION... Moderate to locally breezy trade winds will continue for the next few days. Brief MVFR conditions are possible mainly along north through east slopes of each island. Elsewhere mostly VFR conditions are expected. There are no AIRMETs in effect at this time. && .MARINE... High pressure northeast of the state will bring moderate to locally fresh trades through most of the week. By this weekend, the high will weaken and move off to the northeast, causing trades to decrease slightly across local waters. A Small Craft Advisory remains in effect through Thursday morning for the windier waters and channels around Maui County and Big Island. No significant south swells are expected during the forecast period. However, a series of small south-southwest and southeast swells will keep south facing shores from going flat. Flat to tiny surf conditions will continue along north and west facing shores through most of the week. East shore surf will be close to seasonal levels through late this week as fresh to strong east northeast trades persist over and upstream of the islands. A fetch of strong northeast winds well off the California coast should bring a small, medium period, northeast swell Saturday into early next week. Some of this swell should wrap into select north-facing exposures as well. Water levels higher than normal around Big Island, combined with the new moon tides, could cause minor flooding issues through Saturday, with peak water levels expected Thursday. Recent observations from Hilo Bay and Kawaihae show water levels getting near or over a foot above Mean Higher High Water (MHHW) / 3 feet above Mean Lower Low Water (MLLW), thus a Coastal Flood Statement remains in effect for the coastal zones around Big Island. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Thursday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Blood AVIATION...Bohlin MARINE...Powell