textproduct: Honolulu

SYNOPSIS

A cold front pushing southeastward down the island chain will stall out over the Big Island tonight. With the exception of the Big Island, post frontal conditions will allow for much drier and cooler conditions through Tuesday. Winds will veer southerly Tuesday night as the next front approaches and become breezy to locally windy on Wednesday. The front is forecast to quickly slide down the island chain Wednesday night into Thursday and bring a line of moderate locally heavy rainfall with it. The week should end cool and fairly dry with trades re- established.

DISCUSSION

Latest visible satellite imagery shows a loosely organized band of low clouds associated with a weakening cold front draped from northeast to southwest across Maui County. Rainfall totals associated with the frontal band have been rather unimpressive with most locations on Kauai and Oahu picking up less than 0.25". Across the western islands, post frontal, winds have already shifted northwest to north gusting to between 20 and 30 mph. As a side note, episode 40 of Kilauea eruptions began this morning. Light winds may allow for hazy skies due to increased VOG across portions Big Island during the short term.

Through tonight, the line of scattered low clouds and moderate showers will creep towards the Big Island as the aforementioned front begins to stall and dissipate. Elsewhere, post frontal subsidence aloft will allow for cool, stable, and dry conditions. Dewpoints are forecast to drop in the mid 50s while overnight lows drop into the mid 60s. By Tuesday, winds will veer to a more typical northeasterly flow, but dry subsident air aloft will remain. Thus, expect mostly sunny skies across smaller islands. Remnant moisture around the Big Island may still result in isolated to scattered showers island wide.

By Tuesday night, winds begin to veer southerly as the next cold front approaches the islands from the northwest. Southerly flow continues to increase in strength on Wednesday and become breezy to windy by mid-day. Wind speeds may meet or exceed wind advisory criteria along ridgetops and areas downslope of elevated terrain. Both the GFS and ECMWF show moisture lifting northward over the western half of the state, ahead of the front, and develop pockets of prefrontal showers. This has been reflected in the latest forecast package. For the eastern half of the state, dry conditions prevail.

The front will approach Kauai Wednesday evening, then quickly slide down the island chain through Thursday. Latest guidance depicts this system to be similar, but stronger, than the one experienced today. An area of moderate to locally heavy rain will likely accompany the front, but flash flooding risk appears limited due to the speedy nature of the system. Breezy to windy south to southwest winds ahead of the front will veer northerly immediately behind the front and once again bring noticeable drier and cooler weather through the first half of the weekend.

AVIATION

Cold front currently exiting Maui County and advancing toward the Big Island. A brief episode of MVFR along the frontal zone will be accompanied by scattered showers followed by a transition to gusty northwest winds. The front will hang up over Windward Big Island potentially allowing showers and periods of MVFR to linger there through tonight. Winds diminish tonight tonight and veer to moderate easterly trades on Tuesday. VFR behind the front.

AIRMET Sierra for mountain obscuration is in effect for Molokai. Sierra may eventually be needed for Maui and the Big Island.

AIRMET TANGO is in effect for tempo mod turb FL220/280 for Kauai and Oahu and adjacent waters but may be expanded to the remainder of the forecast area this afternoon. Above FL280, SIGMET UNIFORM for severe turbulence is currently in effect for a portion of the area.

MARINE

A front moving across the islands this afternoon will stall and dissipate just east of the Big Island tonight. Another front will move west to east across the islands Wednesday into Thursday. A passing high pressure system far north of the islands will bring back easterly trade winds from Friday through Sunday.

An extra large long period northwest swell will produce warning level surf for exposed north and west facing shores through Tuesday. A High Surf Warning is posted for these areas, and along with a High Surf Advisory for the west facing shores of Big Island through Tuesday. A Small Craft Advisory is also in effect through Tuesday for most coastal waters exposed to the large northwest swell.

Another extra large northwest (320-330 degree) swell will build into the region by Thursday, likely producing another round of warning level surf along exposed north and west facing shores lasting through Friday, and lingering near advisory levels Saturday before another reinforcement Sunday.

Surf along east facing shores will remain small through the first half of this week due shifting wind directions from the passing fronts, while no significant swells are expected to impact the state from the south.

HFO WATCHES/WARNINGS/ADVISORIES

High Surf Warning until 6 PM HST Tuesday for Niihau-Kauai Leeward-Waianae Coast-Oahu North Shore-Maui Windward West-Kauai North-Molokai Windward-Molokai North-Molokai West-Maui Central Valley North-Windward Haleakala.

High Surf Advisory until 6 PM HST Tuesday for Kona-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.

Small Craft Advisory until 6 PM HST Tuesday for Maui County Leeward Waters-Maalaea Bay-Pailolo Channel-Alenuihaha Channel- Big Island Windward Waters.