Issued: Feb 20, 2017 3:39 AM HST
Breezy trade winds can be expected through the work week as a series of high pressure areas build north of the state. Clouds and showers will favor windward and mauka areas, with showers spilling over into leeward locations from time to time. Winds will diminish over the weekend as an area of low pressure develops northwest of the island chain.
Currently at the surface, a 1029 mb high is centered around 625 miles north-northwest of Kauai, with a weak and dissipating front south of the Big Island. This is driving a breezy to locally windy trade wind flow across the island chain early this morning. Infrared satellite imagery shows mostly cloudy conditions across windward areas, with partly cloudy skies in most leeward locales. Meanwhile radar imagery and rain gauge observations indicate only very light showers or mist moving into windward areas this morning, with rain free conditions over leeward locales. Main short term concern revolves around the breezy to windy conditions over the next few days.
Today through Wednesday, A series of high pressure areas will build north of the island chain through the period, maintaining breezy to locally windy trades through the period. A dry airmass with precipitable water (PW) values generally at or below 1 inch will keep shower activity light and limited primarily to windward and mauka areas through tonight. A bit of an increase in windward and mauka showers is expected Tuesday through Wednesday as an upper level trough moves overhead. This will result in rising inversion heights and sending some light showers into leeward areas from time to time.
The mid and upper level cloud cover has cleared Oahu and Kauai, with the thinning band of mid/high clouds currently moving through the eastern islands. Overall, partly to mostly cloudy skies are expected in windward areas through the period, with clear to partly cloudy skies in leeward locales.
The current Wind Advisory remains remains in effect for Lanai, Kahoolawe, and for areas over and downwind of the Kohala mountains on the Big Island through 6 PM this evening. Winds have increased in areas south of Volcano overnight, so the advisory has been expanded to include this area as well through 6 pm. Winds are expected to drop below advisory levels in these areas tonight.
Wednesday night through next Sunday, High pressure north of the state will keep moderate to breezy trade winds in place through Friday, with the trades diminishing over the weekend as an area of low pressure develops to the northwest of the island chain. A dry airmass will remain in place across the state for the tail end of the work week and through next weekend, with PW values remaining at or below 1 inch. As a result, showers should remain limited primarily to windward and mauka areas through the period. There may be an increase in showers by early next week as some tropical moisture begins to work its way northward from the Intertropical Convergence Zone (ITCZ). Confidence remains low regarding the exact details at this time given considerable disagreement between the reliable model guidance.
A strong high pressure system located north of the islands will continue to produce strong and blustery northeast trade winds through most of the new week. Also, a strong low level inversion is slated to be based between 45 hundred and 6k feet at least through tonight. These two features will produce tempo moderate turb below 8k feet.
Turbulence models were suggesting a bit of mid to high level turbulence between 18k and 30k feet mainly over the central islands. This area of turb should be easing off by the next aviation package (16Z).
Remnant moisture from a front has eased up on windward Big Island. Thus AIRMET Sierra for mountain obscuration was lowered around midnight. There is plenty of low clouds coming in with the northeast trades. However, these clouds appear to be high based around 45 hundred feet.
With the northeast trades in place, scattered light showers are the rule-of-thumb favoring the windward and mountain areas of all of the larger islands. Expect some brief MVFR ceilings with these showers. Restriction to vis from the showers is not expected. Otherwise, VFR is the prevailing flying condition. A band of mid to high level clouds continue to thin as it passes through the eastern part of the island chain.
No other AIRMETs are expected.
The Sunday evening ASCAT pass did not find any gales in the Alenuihaha Channel, but did find some areas of 30-32 kt winds, and high-resolution models suggest that winds may increase a bit more today in the typically windy zones around Maui County. Thus the Gale Warning will remain posted through today for the Pailolo and Alenuihaha Channels and Maalaea Bay. Small Craft Advisory conditions will continue for all other waters due to the combination of strong winds and high/rough seas, and the advisory has been extended for those waters through Tuesday. The areas currently in the Gale Warning will need to be added to the advisory as well once the gales end.
In addition to the winds and rough seas, a north-northwest swell will remain near peak levels into this morning, then gradually ease later today through Tuesday. Significant wave heights at the nearshore buoys and at buoy 51101 are running somewhat above the latest wave model guidance. This swell will continue to produce advisory-level surf along north and west facing shores of the smaller islands today. With swell rising well above guidance levels at the Hilo buoy, we have decided to err on the side of caution and add the north facing shores of the Big Island to the high surf advisory for today as well.
Surf along east facing shores will gradually rise through midweek, and may reach advisory levels by Tuesday night or Wednesday.
On Wednesday, a moderate, long-period west-northwest swell associated with a developing gale east of Japan is expected to fill in, peaking late Wednesday through Wednesday night. This swell will gradually ease Thursday, before a reinforcing swell from the same direction, but longer period, builds in late Thursday night and Friday. If this source comes in slightly higher than predicted, advisory-level surf along north and west facing shores will be possible Wednesday and Wednesday night. Advisory-level surf looks more likely with the Friday swell event.
High Surf Advisory until 6 PM HST this evening for Niihau, Kauai Windward, Kauai Leeward, Oahu North Shore, Oahu Koolau, Molokai, Maui Windward West, Maui Central Valley, Windward Haleakala, Big Island North and East.
Wind Advisory until 6 PM HST this evening for Lanai, Kahoolawe, South Big Island, Big Island North and East, Kohala.
Small Craft Advisory until 6 PM HST Tuesday 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 PM HST this evening for Maalaea Bay, Pailolo Channel, Alenuihaha Channel.