textproduct: Honolulu

SYNOPSIS

A strong surface high will continue to build north of the state today and help bring locally windy trade winds through Saturday afternoon. A drier and more stable air mass will also settle in over the state. Trades will ease back to more typical summertime breezy levels Sunday into early next week as the surface high weakens. Isolated to scattered showers will mainly affect windward locations with dry weather expected for leeward areas.

DISCUSSION

This morning's IR satellite imagery loop shows pockets of deep convection around 500 miles northwest of Kauai. This area of disturbed weather is associated with the remnant low of post TC Fausto. Meanwhile, closer to home, scattered low clouds can be seen pushing towards the windward coasts from the northeast, upstream of the Hawaiian Islands. A few showers were picked up overnight on radar, but nothing really of note. A handful of reporting stations received a few hundredths of an inch of accumulation. As a drier and more stable atmosphere advects in across the state today, expect scattered clouds and isolated showers to affect mainly windward locations while leeward areas remain dry. The 12Z RAOB sounding from Hilo showed a rather shallow inversion height near 5500 feet. Model cross sections show this inversion height falling to near 5000 feet by this afternoon.

A ridge of surface high pressure far north of the state is expected to strengthen today. In response, local pressure gradients will tighten. This, along shallow inversion heights, will bring breezy to windy trade winds to the islands. A Wind Advisory has been issued for portions of all islands, except for Kauai, from Noon today through late Saturday afternoon. Winds will accelerate downslope, near mountain tops, and ridges, through gaps in the terrain, and in areas typically exposed to trade winds. Portions of Kauai, especially across ridge tops and in the lee of the mountains, may need be added to the advisory starting late this evening. The aforementioned area of high pressure should drift eastward on Sunday, loosening local pressure gradients, and easing trades back down to typical summertime levels.

Early to mid-next week, trades will further ease as Tropical Storm Genevieve weakens into a post tropical depression and tracks far northeast of the state, disrupting trade wind flow. Both the GFS and ECMWF prog an upper level trough, or closed low, to develop just northwest of Kauai. If this comes to fruition, expect a steady increase in mid and upper level moisture/clouds drawn northward from the tropics ahead of this feature.

AVIATION

Moderate to breezy trade winds will prevail through the period. Occasional MVFR ceilings and possible lowered visibilities over windward and mauka areas within brief, heavier showers.

No AIRMETs are currently in effect. Strengthening lower level trades will warrant an AIRMET TANGO across and immediately S through W of high terrain later today.

MARINE

Strong trades develop across all nearshore marine zones this afternoon as governing high pressure strengthens and migrates south toward the islands. The existing Small Craft Advisory has therefore been further expanded to capture all nearshore waters.

Fading S swell will be followed by the occasional small, medium period pulse of energy out of the southerly quadrant during the next several days. This will maintain surf slightly below the seasonal average.

Small long period forerunners emanating from Hurricane Genevieve in the East Pac have registered on offshore NDBC buoys with some indication of this energy at the nearshore Hilo CDIP buoy as well. This swell will remain small, on the order of a couple feet, as it peaks Friday into Friday night and then fades heading into early next week. This swell will be mixed with building trade wind swell and wind wave action as strong trades become established. N shores remain tiny to flat as do W facing shores except for locales exposed to medium period S swell.

FIRE WEATHER

Trades will increase in strength through the day today. In addition, a drier and more stable airmass will drop inversion heights to around 5,000 ft this afternoon into Saturday that could lead to gusty downslope winds and low relative humidity values. With the lowered inversion heights, chances of precipitation will be subdued and limited to windward areas. While KBDI will remain below the critical thresholds, this hot, dry and windy pattern could make for some near critical fire weather concerns, especially for areas above the inversion height and downslope of ridges. Trades are expected to return to more normal moderate to locally breezy levels Sunday into early next week.

HFO WATCHES/WARNINGS/ADVISORIES

Wind Advisory from noon today to 6 PM HST Saturday for Waianae Mountains-Lanai Mauka-Kahoolawe-Maui Leeward West-Kohala-Big Island Interior-Koolau Leeward-Molokai North-Molokai West- Molokai Leeward South-Lanai Windward-Lanai Leeward-Maui Central Valley North-Maui Central Valley South-South Haleakala-Big Island South-Big Island Southeast-Big Island North.

Small Craft Advisory from noon today to 6 PM HST Saturday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-Oahu Windward Waters-Oahu Leeward Waters.

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