High pressure north of the state will maintain moderate trade winds through Wednesday. The trades will strengthen Wednesday night and Thursday, then remain strong through the weekend. Showers will favor windward and mountain areas, with an increase in showers expected late this week into the weekend as the trade winds strengthen and a weak upper level trough develops over the region.


Dry conditions prevail across much of the state on this Monday evening. The exceptions are parts of windward Maui and windward sections of the Big Island, where rainfall amounts between one quarter and one inch have been measured at some gauges during the past six hours. Early evening infrared satellite images show a band of low clouds associated with remnants of an old frontal boundary sinking slowly southward over the eastern end of the state. These clouds have cleared south of Kauai, Oahu and Molokai, allowing for drier conditions on those islands. The leading edge of another frontal remnant cloud band is currently located about 60 miles north of Kauai and about 100 miles north of Oahu, and these clouds are also moving slowly southward. Surface analysis depicts a 1028 mb high far north of the state, with moderate to locally breezy trade winds prevailing over the islands. Aloft, a strong ridge is centered several hundred miles to our northwest and is maintaining stable conditions over the islands. The 00Z Hilo sounding measured PW of 1.32 inches with the inversion based near 8500 feet, while the 00Z Lihue sounding found a below normal PW value of 0.97 inches and the inversion based near 5500 feet. MIMIC-TPW satellite imagery shows narrow stripes of slightly enhanced moisture with estimated PW values up to 1.5 inches along the frontal remnants over the Big Island and just to the north of the state. Overnight, showers may decrease late over the windward sections of the Big Island and Maui, as the frontal remnant cloud band shifts south of those islands. At the same time, showers will probably increase late tonight over windward parts of Kauai and Oahu as the next remnant frontal cloud band moves south into those islands. Leeward areas will remain drier, although a few showers may spill over into those sections of the smaller islands. Have made minor updates to the gridded/text forecasts to reflect the above thinking. High pressure far to our north will maintain moderate trade winds for Tuesday into Wednesday. A couple of additional cloud bands associated with frontal remnants will move south through the state during this time, causing periodic increases of shower activity mainly over windward areas. The leeward Big Island will continue to see the typical diurnal pattern of clouds and widely scattered showers forming over the slopes during the afternoons, followed by clearing at night. Trade winds will increase beginning Wednesday afternoon or evening through the later part of the week, as a new high pressure area builds north of the state. This high will sink slowly southward into the weekend, maintaining strong trade winds with windy conditions over the islands. Persistent upper level ridging will continue to keep a cap on the trade wind showers through Thursday night, with only light to moderate rainfall amounts expected mainly over windward areas. A weak mid/upper level trough is expected to develop over the state beginning Friday and continuing into the weekend. The resultant cooler temps aloft will increase instability and allow for increased shower coverage and intensity beginning Friday or Friday night and into the weekend. With the strong trades and increased vertical cloud depth, expect a wet trade wind regime over the weekend and into early next week, with scattered showers readily spilling over into leeward areas.


Isolated to TEMPO MVFR conditions are likely to persist over windward and mauka areas, mainly from Oahu to the Big Island, through the evening hours and overnight as moisture from an old front continues to affect the isles. However, VFR will prevail generally. An AIRMET for mountain obscuration remains in effect for the northeast section of the Big Island. The one for low level turbulence has been cancelled since the trade winds have eased.


A small craft advisory remains posted for the typically windier locations around Maui County and the Big Island through Tuesday. Winds in these areas may temporarily drop below advisory levels Tuesday night and Wednesday. Another high pressure area will build north of the state once again beginning late Wednesday through the rest of the week, bringing strong trade winds back to the islands. Another round of near gales in the windier marine zones and advisory-level surf along east facing shores will be possible from Thursday night or Friday into the weekend. Surf along east-facing shores will ease through Wednesday with values remaining below advisory levels. A new long-period northwest swell will fill in later tonight, peak late Tuesday through Tuesday night, then gradually ease later Wednesday through Friday. Surf heights will respond, but should remain well below advisory levels through the peak. A small subsiding south swell will remain into Tuesday, translating to a slight bump in wave heights along south facing shores.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.



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