Breezy to locally windy trade wind pattern persists through the week. Moisture embedded in the trades will periodically deliver clouds and showers to windward and mauka areas. Wetter weather is possible this weekend.
Strong subsidence in full swing this morning as evidenced by the rapidly strengthening and lowering trade wind inversion on the most recent soundings out of Lihue. This subsidence is driven by building mid-level ridging and strong dry advection in the 850-700mb layer supporting dewpoint depressions on the order of 50C at 700mb. This supports current wind gust observations ranging between 35 mph along the Waianae Coast of Oahu to 40-50 mph in the lee of the West Maui Mountains. Large scale conditions will favor maintenance of downsloping through today. Meanwhile, the latest ASCAT pass indicates widespread sustained wind observations just shy of 30 kts over the open water immediately upstream of the islands, suggesting that the full suite of guidance is undersimulating winds by several knots. No reason to alter the existing Wind Advisory at this time. Leeward Maui and Oahu will be monitored for potential areal expansion as the morning progresses. Active subsidence will ease tonight into Wednesday, though the mid-level dry airmass will remain in place in support of a strong inversion. Gradient winds are modeled to undergo little change during the next 36 hours, an extension in time to the Wind Advisory will be a decision point today as well. Strong and stable trades continue through Thursday before static stability begins to diminish on Friday.
The week will otherwise be characterized by a rather slowly evolving large scale pattern that will ultimately lead to potential for several days of wet and unstable trades this weekend into early next week. Presently, upper troughing and convergent SE flow in the low levels maintains a steady moisture feed into a complex of thunderstorms centered near 15N/145W. Pressure falls and deepening cyclonic flow associated with evolving troughing west of the Hawaiian Islands will allow this moist SE flow to extend northwestward over the islands Friday into the weekend. Saturday and Sunday potentially feature a round of moderate dynamic forcing coupled with adequate left exit support superposed with moderate to strong moist trades in the lower levels. A flash flooding threat may develop during this time, but forecast confidence will be largley contingent on the expected strength of trades which will in turn modulate forward motion of showers. At this time, guidance indicate the islands residing along the gradient between stronger trades to the east and light SE flow to the west with plenty of room for error in either direction. Mid-level lapse rates are adequate but not impressive suggesting thunderstorms remain nothing more than an isolated threat. Certainly a scenario worth monitoring as the end of the week draws closer.
Strong trade winds will prevail with winds beginning to veer east southeast by the end of today. Passing showers will primarily impact windward sides of the islands, occasionally reaching leeward sides. AIRMET Sierra is posted for tempo mountain obscurations above 2500 feet for the Big Island.
AIRMET Tango is also in effect for tempo moderate turbulence below 7000 feet over leeward sides of the islands.
A strong high pressure system far north of the Hawaiian Islands will continue to drift farther south through Wednesday and then weaken from Thursday onward. This closer proximity to the islands will keep strong and gusty trade winds in the regional forecast through at least Wednesday. A Gale Warning was issued for windier waters and channels around the island of Maui as satellite winds showed a large area of gale force winds last night. The Small Craft Advisory remains in effect for all Hawaiian Coastal Waters outside of the gale warning area. A slight decrease in trade wind speeds will develop from Thursday into Friday as the high weakens briefly, before another strong high develops far north of the state later this weekend.
Surf heights along east facing shorelines will remain solidly within High Surf Advisory (HSA) criteria through Wednesday, driven primarily by a large and persistent fetch of fresh to strong trade winds upstream of the islands. The HSA will continue through Tuesday night and an extension through Wednesday is looking likely as strong upstream trades are expected to persist.
Surf will remain small along north, west and south facing shores through Saturday, as no significant swells are forecast into the weekend.
In the extended range forecast, forerunners from the next moderate to large, long period north (010-020 degree) swell appear to arrive by late Sunday night, building swiftly to advisory levels through next week Monday, and then slowly declining into the middle of next week. A Harbor Surge Marine Weather Statement may be required for north facing harbors, especially for Kahului and Hilo harbor.
High Surf Advisory until 6 AM HST Wednesday for Olomana-Maui Windward West-Kauai East-Kauai South-East Honolulu-Koolau Windward-Molokai Windward-Molokai Southeast-Windward Haleakala- Kipahulu-Big Island Southeast-Big Island East-Big Island North.
Wind Advisory until 6 PM HST this evening for Waianae Mountains- Lanai Mauka-Kahoolawe-Maui Windward West-Kohala-Big Island Interior-Koolau Leeward-Molokai Windward-Molokai Southeast- Molokai North-Molokai West-Lanai Windward-Lanai Leeward-Lanai South-Maui Central Valley North-Maui Central Valley South- Windward Haleakala-South Haleakala-Big Island South-Big Island Southeast-Big Island North.
Small Craft Advisory until 6 PM HST Wednesday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters- Kauai Channel-Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-Maui County Leeward Waters- Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters.
Gale Warning until 6 AM HST Wednesday for Maalaea Bay-Pailolo Channel-Alenuihaha Channel.
