textproduct: Honolulu

SYNOPSIS

A high pressure ridge to the north of the state will remain locked in place for the foreseeable future keeping Tropical Storm Pena moving in a westerly direction, passing well south of the Hawaiian Islands. Expect a transition to breezy trade winds today with drier trends through the weekend, lasting into the first half of next week. The next best chance for increasing statewide shower activity arrives from next week Thursday to Friday as an unsettled cloud band associated with a dissipated cold front moves in from the north.

DISCUSSION

The satellite imagery this morning shows more stable stratocumulus clouds east of the Hawaiian Islands riding in on the trade winds. These low level cloud features are more stable indicating stronger subsidence aloft and lower trade wind temperature inversion heights. This upstream stability validates our drying trends though Sunday as the upper low that was anchored west of the state dissipates and the deep tropical moisture surge associated with the passing easterly wave wanes.

Tropical Storm Pena remains roughly 525 miles south-southeast of South Point on the Big Island of Hawaii. Pena will continue on a east to west track under the steering influence of the lingering high pressure ridge north of the state keeping the tropical storm impacts well south of the island chain. Easterly winds may approach wind advisory thresholds in some terrain favored areas. However, at this time we are not expecting to issue wind advisories as Tropical Storm Pena passes south of the state.

Large scale atmospheric downward vertical motions (subsidence) over the next several days will cause the trade wind temperature inversion heights to fall, lowering cloud heights, and limiting shower activity from later today through Wednesday. Temperature inversion heights will range from 6,000 to 7,000 feet elevation during this time period, high enough for brief passing showers mainly along windward mountain ranges, favoring the overnight to early morning hours. Rainfall amounts over Maui and the Big Island will trend lower as compared to the past several days.

The next best chance for increasing statewide shower activity arrives from next week Thursday to Friday as an unsettled cloud band associated with a dissipated cold front moves in from the north. Expect northern and eastern slopes of all islands to see additional beneficial rainfall as breezy easterly trade winds lift these unsettled clouds up island mountain slopes.

AVIATION

Moderate to locally breezy trade winds will persist through the period. Pockets of higher moisture riding in on the trades early this morning will guarantee occasional lower decks falling to low VFR or MVFR flight categories along with more frequent windward showers especially at Hilo (PHTO). Better organized rain clusters passing over windward terminals this morning will produce more frequent periods of MVFR in both lowered ceiling and visibility. Conditions will begin to slowly improve this afternoon as drier air moves in from the east.

AIRMET Sierra is in effect for mountain obscuration across windward Big Island, Maui, Molokai and Oahu. Sierra will likely will allowed to expire by noon with lifting decks to VFR levels.

AIRMET Tango remains in effect for moderate turbulence within the lee of higher terrain.

MARINE

Fresh to strong trade winds will prevail through through the remainder of this weekend as high pressure dominates north of the state and Tropical Storm Pena moves westward, several hundred miles south of the state. The Small Craft Advisory (SCA) has been extended through Sunday night for most Hawaiian Waters due to a combination of winds and elevated seas. The Big Island windward waters were dropped due to wind speed guidence falling just below SCA criteria. Winds are expected to ease slightly late Monday and Tuesday as the ridge to our north erodes and Pena moves away to the southwest. The SCA will likely be trimmed back to the typical windy waters around Big Island and Maui at that time. Trade winds are expected to strengthen again on Wednesday.

A small to moderate, medium period, northwest swell will continue to affect north and west facing shores today. A larger reinforcing medium- period swell out of the north- northwest (325 to 340 degree) will arrive by late this evening and fill in tonight. Surf could reach advisory thresholds during the peak of the swell late tonight into Sunday morning. Another large northwest to north- northwest swell is set to arrive late Wednesday into Thursday.

A small south-southwest swell should produce surf slightly above seasonal average today. A tiny pulse from the south may maintain south shore surf near seasonal average Sunday and Monday, followed by background level surf through the remainder of the week.

Rough surf along east-facing shores will hold at or above seasonal average through this weekend. Surf will decrease slightly by early next week as trades begin to ease.

FIRE WEATHER

A high pressure ridge to the north and Tropical Storm Pena passing south of the islands will keep breezy trade winds in the forecast with decreasing humidity levels. Fire weather conditions will remain below critical thresholds into next week. Temperature inversion heights today near Maui and the Big Island will drop into the 6,500 to 7,500 foot elevation range.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory until 6 AM HST Monday for most Hawaiian coastal waters and channels.