textproduct: Honolulu

SYNOPSIS

A plume of shallow moisture lingering in a light to moderate trade wind flow will maintain increased cloud cover through morning, while wet conditions persist over mainly windward Big Island. An approaching disturbance aloft may trigger a few heavy showers this afternoon and tonight, mainly over Kauai and Oahu. The tail end of a front will move down the island chain late Sunday through Monday, bringing breezy northeasterly trades and drier air in its wake. Breezy easterly trades will bring periods of windward and mauka showers through the rest of the week.

DISCUSSION

Stubborn shallow moisture continues to produce enhanced cloud cover over the island chain with somewhat wet conditions lingering on windward Big Island this morning. The surface trough that affected the state during the past few days is now over 50 miles southeast of Big Island and drifting away as light to moderate trade winds remain in place over the state. Deeper moisture pooled along this feature will continue to produce somewhat wet conditions across windward Big Island this morning, with a decrease in shower activity expected this afternoon as moisture decreases. A lingering band of shallow moisture continues to stretch across the remainder of the state and extends to an area of thunderstorms 100 to 500 miles west of Kauai. Despite high humidity, shower activity is expected to be limited from Maui to Kauai this morning, but as the upper level trough generating the thunderstorms to the west edges closer to the islands this afternoon, a few heavy showers could develop on Kauai and possibly Oahu.

Light trade winds will produce mainly windward rainfall from Big Island to Maui County tonight into early Sunday morning, while the above mentioned upper level trough passes just north of the state and possibly generates more shower activity near Kauai and Oahu. The ECMWF is suggesting higher chances of rainfall over the western end of the island chain, while the GFS is keeping the heavier showers away from the islands. As a result, confidence is lower than usual.

A shallow front will break apart as it moves down the island chain late Sunday and Sunday night. While this feature will deliver some rainfall to windward and north facing terrain, the main impact will be the development of breezy and gusty northeasterly trade winds from west to east. Deep high pressure building behind the front will usher in a drier and more stable air mass, and with dew points potentially dropping into the lower 60s or may even the upper 50s, this will feel more like the first shot of winterlike conditions than just relief from the recent humidity.

A breezy and stable trade wind flow will continue through at least the end of the work week as high pressure holds north of the state. Dew points will remain quite low on Tuesday, then gradually rebound closer to normal. Expect rainfall to be largely focused across windward slopes, with passing light rainfall leeward.

Heading into next weekend, focus returns to the tropics again. While the details are out of agreement, the GFS and ECMWF are showing possible tropical cyclone development far southeast of the state late in the week with some chance of a tropical cyclone being near or south the islands next weekend. The National Hurricane Center continues to monitor this area, maintaining a medium (40 percent) chance of development over the next 7 days.

AVIATION

A trough to the west and ridge to the east will maintain easterly trade winds through the morning, with significant differences in model solutions later by mid morning. Light showers and clouds will focus over primarily windward and mountain areas this morning. The exception will be windward Big Island, where increased moisture will linger through the forecast period, keeping lower ceilings and reduced visibility in place. This afternoon and evening's conditions will depend on the progression of the trough to the west. Half of our model solutions depict this feature bringing deeper moisture over Kauai and moving down to Oahu this afternoon through tonight, along with veering winds to the southeast. This solution would mean more showers and low ceilings/reduced visibility over Oahu and Kauai tonight. The other half of our models show drier conditions with light easterly winds. There is also the chance for some pop up afternoon showers today as low level moisture associated with the trough lingers.

AIRMET Sierra for mountain obscuration remains in effect abv 020 for windward areas of the Big Island, Maui, and Molokai. This could remain through the early morning before improving late morning.

MARINE

High pressure to the north will bring moderate to fresh trades to the region today. Northeast winds are forecast to strengthen behind a trough dropping south across the islands on Sunday, which may require a Small Craft Advisory for all coastal waters. An incoming north-northwest swell combined with strengthening trades will push seas in excess of 10 feet for exposed waters. Moderate to fresh northeast trades remain in place through much of the week as high pressure sits north of Hawaii.

The current small, short period north-northeast swell will maintain small surf along north- and east-facing shores today. The forerunners from a moderate, long-period northwest swell are expected to arrive this afternoon/evening, with the swell building quickly overnight. By Sunday, advisory level surf is expected for north and west facing shores, which is expected to continue into Monday. The swell is may shift slightly more northerly briefly build further on Monday before dropping on Tuesday. Depending on the exact direction, a Marine Weather Statement may eventually need to be issued due to the potential for harbor surges at Kahului and Hilo during that time. Another advisory level northwest swell is possible Thursday into Friday.

The current moderate, medium period south swell will gradually decline through the weekend. Surf above seasonal average returns to seasonal average on Sunday as the south swell energy fades. During the first half of next week, south shore surf will return to below seasonal averages.

East-facing shores will see an increase in trade wind swell as northeast winds return on Sunday. Surf along east-facing shores will increase through Monday night and conditions will be choppy as trades sustain through much of the week.

FIRE WEATHER

The anomalously wet conditions during the past few months and the rainfall from the past few days has kept the Keetch-Byram Drought Index (KBDI) below 500 across nearly all of the state. Fire weather concerns will be low through early Sunday as trade winds remain light and humidity elevated. Breezy and much drier trade winds will develop by Monday, but since KBDI will remain suppressed, fire weather conditions will be moderate.

HFO WATCHES/WARNINGS/ADVISORIES

None.