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FXHW60 PHFO 030135 AFDHFO

Area Forecast Discussion National Weather Service Honolulu HI 335 PM HST Thu May 2 2024

SYNOPSIS
Trade winds will strengthen today, becoming breezy Friday through the weekend. Clouds and showers will favor typical windward slopes, with an increase in showers expected this weekend through the first half of next week as a disturbance aloft moves over the state.

DISCUSSION
Easterly trade winds have been on the increase through the day as a surface trough just northwest of Kauai continues to weaken and a 1030 mb surface high remains to the far northeast. Meanwhile, an upper level low is deepening approximately 600 miles northwest of Kauai. Satellite and radar imagery show partly to mostly cloudy skies across the islands with a band of showery low clouds beginning to move into windward areas this afternoon. Some leeward areas are also seeing some shower activity spilling over the mountains, especially over eastern portions of Oahu. Even so, relatively stable conditions remain over the state, keeping rainfall totals around a tenth of an inch or less over the last few hours and highly localized. Trade wind speeds are forecast to increase into the breezy to locally windy range across the islands on Friday, then continue through the weekend as high pressure strengthens and settles in far northeast of the state. Expect the strongest winds over the windier areas of Maui County and the Big Island.

Guidance continues to show the aforementioned upper low stalling to the west of Kauai this weekend, then slowly moving eastward across the state early next week. As this happens, expect a boost in to our trade wind showers, especially during the overnight and early morning hours, with a few brief downpours possible through the first half of next week. Some showers could drift over into leeward areas as well, due to the stronger winds. Details are still uncertain, but windward and mauka areas could become quite showery through early next week, especially across the western end of the state where the best instability exists. Some models also hint at an outside chance for some isolated thunderstorms during this time period.

Expect a return to a more typical moderate to breezy trade wind pattern by Wednesday, as the upper low weakens and moves away from the state and high pressure weakens to the north.

AVIATION
Moderate to breezy easterly trades will continue to strengthen into Friday as high pressure builds in from the northeast. A plume of moisture riding in on the trades is responsible for bringing low clouds and scattered showers to most windward areas this afternoon. VFR conditions will generally prevail, except for isolated areas of MVFR conditions in any heavier showers that may develop. Best chance for MVFR conditions will be during the overnight hours when shower activity is expected to become more scattered in coverage.

With the increasing wind speeds across the state today and into tomorrow, AIRMET Tango may be needed by this evening for tempo moderate turbulence below 8000 feet downwind of island terrain.

AIRMET Sierra for tempo mountain obscuration is in effect for windward portions of the island chain as cloud and shower coverage increases this afternoon, and will likely be needed during the overnight hours as well due to another uptick in shower activity.

AMD NOT SKED in for Midway due to missing wind speed and direction.

MARINE
Moderate to locally strong easterly trade winds will gradually increase through Friday, becoming fresh to locally strong as high pressure strengthens and settles far northeast of the state. These stronger trades will then continue through the weekend. A Small Craft Advisory (SCA) remains in effect for typical windy waters around Maui and the Big Island through early Monday morning.
Additional waters will likely be added to the SCA on Friday as trade winds continue to strengthen and expand in coverage across additional coastal zones.

Tiny surf will persist along north and west facing shores through much of the day on Friday. A small, long period northwest swell is expected to fill in late Friday and peak Saturday, bringing small surf along north and west facing shores. Another small, long period northwest swell will fill in late Sunday, maintaining small surf along north and west facing shores into early next week. Small background south swells will continue into Saturday, providing tiny surf for south facing shores. A small, long period south swell may arrive Sunday providing a boost in surf along south facing shores into early next week. Surf along east facing shores will gradually become more rough and choppy into this weekend as stronger trades return.

HFO WATCHES/WARNINGS/ADVISORIES
Small Craft Advisory until 6 AM HST Monday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters.

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