SynopsisThe start of a drier trade wind pattern is on tap for this afternoon, and is expected to last through most if not all of the upcoming week. Breezy, locally gusty conditions will persist through Sunday before easing off slightly between Sunday night and Tuesday. Even lighter trades are expected over the second half of next week as a front threatens the islands. These trade showers will be favoring the windward and mountain areas, with a few of the showers drifting into the leeward areas of the smaller islands.
DiscussionOne more batch of showers to deal with before the start of a drier trade wind regime. So far this batch of showers has reached Maui but appears to be struggling further westward. The ECMWF and GFS models are hinting that this shower area to dissipate over Maui and the Big Island this morning. Mid level ridging will settling over the islands this morning, aiding in this drier and stable environment. It is forecast to stick around the islands through the new work week. Kauai is still getting a good bit of trade showers this early Saturday morning, but satellite shows a thinning out of the low cloud field upwind of the island. So, we are anticipating a drier sunrise there. Under this trade wind regime, the showers will increase during the overnight and early morning hours, and be rather dry by mid-morning or the afternoon hours.
Breezy trade winds should last another day or so as a tight pressure gradient remains over the islands. The models are pointing to a slightly stronger and stiffer trade wind flow today and tonight. So the winds for these 2 periods have been beefed up, especially in the windier areas of the Big Island such as the Waimea saddle and parts of the Puna district. These winds have the potential of reaching wind advisory criteria which is sustained winds of 30 mph at the lower elevations. So we will be monitoring the situation closely. This gradient should start relaxing about Sunday with trades lowering to moderate to locally strong by Tuesday. The trades may rebound briefly to locally strong about Wednesday as a 1025 mb high pressure system passes due north of the islands. This high scoots off to the east rather fast where the trades will fall off to light to moderate speeds by Friday night. This is due to a dissipating cold front approaching the islands from the northwest.
The latest water vapor imagery shows an upper level trough about to move through the central islands from the north.
AviationBrisk easterly trade winds will persist across the state today, with clouds and showers focusing on windward and mauka areas. Some showers will spill into leeward sections of Kauai and Oahu at times this morning. Airmet sierra is posted as of 12Z for windward sections of Kauai, Maui and the Big Island, due to tempo mountain obscuration. A drying trend is forecast across the state by this afternoon, with just passing light showers over windward areas.
Airmet tango for moderate turbulence below 7000 feet immediately south and west of the higher terrain remains in effect for all islands, and will continue to be necessary through today.
MarineForerunners from a new northwest to north-northwest swell have reached the Hanalei buoy off kauai's north shore about an hour ago with a swell height of 6 feet and about 19 sec period. Oahu's north shore should be getting 15 footer by noon and 20 footer this afternoon.
The direction of this swell has some NW component which will likely catch a part of oahu's leeward coast. Therefore, a high surf advisory now include the west facing shores of Oahu. The strong trades will continue to produce rough surf along east facing shores, but surf heights are expected to remain just below advisory levels. The rest of the surf forecast looks good.
We have added the Maui leeward waters to the small craft advisory due to winds starting this morning as per the high resolution wind model. We will be trimming back the marine zones under the SCA about Sunday night.
HFO Watches/Warnings/AdvisoriesHigh surf advisory from 6 am HST today to 6 pm HST Sunday for north and west shores of Niihau Kauai Oahu and Molokai.
High surf advisory for the north facing shores of Maui, and the Big Island.
Small craft advisory until 6 pm HST Sunday for all Hawaiian waters except windward Big Island waters.
DISCUSSION AND MARINE...LAU