Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
964 FXHW60 PHFO 040137 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 337 PM HST Mon Jun 3 2024 .SYNOPSIS... Trade winds will persist through Wednesday, then diminish and become light and variable for the second half of the week. The island atmosphere will be unstable through Tuesday, so windward trade showers will be a little more active than normal. Additionally, daytime heating of the slopes on the Big Island will bring the potential for an afternoon thunderstorm. A trend toward much drier weather will start Wednesday, and continue through the weekend. && .DISCUSSION... Breezy and somewhat wet trade wind weather through Tuesday will trend much drier after mid-week as winds diminish and a ridge aloft builds over the area. In the meantime, a mid- and upper-level low centered just E of the islands will drift W tonight, stall near the islands through Tuesday, then move E on Wednesday. Although the atmosphere is not especially moist, the low has prompted the development of isolated (and somewhat unusual) high-based thunderstorms within 200 miles E of the islands, due to steep mid- and upper-level lapse rates. Afternoon soundings highlight the large amount of CAPE above ~10-12 thousand feet, with a sturdy subsidence inversion near 8000 ft keeping surface-based parcels from tapping into this instability aloft. The exception is on the Big Island, where afternoon heating of the upper slopes may drive the development of an isolated thunderstorm. Outside chance that a few more high-based thunderstorms occur overnight E of the islands, and a slight chance of thunderstorms has been added to windward waters. Otherwise, windward showers may be a little more active than normal. As the low moves E Wednesday, a strong mid-level ridge will build over the area from the NW, leading to a very stable island atmosphere, thereby significantly lowering inversion heights/rainfall chances. A surface ridge N of the islands will remain nearly stationary through Tuesday, supporting locally breezy trade winds. On Wednesday and Thursday, unseasonably strong low pressure rapidly developing N of the area will weaken the high and displace the ridge southward near the islands, with winds becoming light and variable Thursday and Friday. The ridge will gradually strengthen and move N over the weekend, and light to moderate trade winds are expected. With relatively light winds and a stable atmosphere, a mostly dry regime is anticipated. && .AVIATION... Breezy to locally strong trades will deliver clouds and showers to windward and mauka zones through the period. Nothing more than isolated MVFR expected. The arrival of elevated instability favors a chance for isolated thunderstorms over interior and upslope sections of the Big Island and Mount Haleakala on Maui both this afternoon and tomorrow afternoon. AIRMET Tango for lee turb remains in effect. && .MARINE... Broad high pressure north of the state will maintain fresh to strong trade winds into Tuesday, and a Small Craft Advisory (SCA) remains in effect for all waters around the Big Island and Maui County and select areas around Oahu and Kauai. Trades will decline late Tuesday and Wednesday as the ridge of high pressure is weakened and pushed southward, and the SCA will will likely be trimmed back to the typical windy waters around the Big Island and Maui. The ridge will erode further and be displaced farther south near Kauai Thursday into Friday, causing the trades to diminish significantly and possibly become disrupted. The SCA will be dropped completely by this time. Increasing moderate trades are expected during the weekend as the ridge lifts northward. An extended run of southerly swell will continue this week and almost certainly through mid June. The current south-southwest swell is peaking today at around 3 feet 15 seconds, leading to surf near the 10 foot High Surf Advisory level. This swell will gradually decline Tuesday into Thursday, followed by a reinforcing south- southwest swell late Thursday and Friday that will produce south shore surf around seasonal average. As this swell lowers, a larger swell will move through during the weekend, boosting surf around the advisory level Sunday and Monday. A potentially larger swell is looking increasingly likely to push surf well above the advisory level late next week. A small northwest swell building today will peak late tonight and Tuesday, then linger into Thursday. A small short-period north- northwest swell should follow later in the week. The fresh to strong trade wind flow is producing elevated seas of 7 to 8 feet at 7 to 8 seconds. As trade winds decline Wednesday through Friday, rough east shore surf will decline well below seasonal average, then remain small through the weekend. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Tuesday for Kauai Northwest Waters-Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-Maui County Leeward Waters-Maalaea Bay-Pailolo Channel- Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Birchard AVIATION...JVC MARINE...Wroe