textproduct: Honolulu

SYNOPSIS

A line of light to moderate showers across the central portion of the state is expected to lift north and dissipate this evening. Light and variable winds will favor some onshore sea breezes through midweek. By the latter half of the weak, light east to southeast winds and quieter weather return to the forecast. This weekend may see a boost in showers as an upper level disturbance approaches from the northwest.

DISCUSSION

A band of mostly light showers has shifted slightly east over the central islands this afternoon, contrary to what most of the hi- res model guidance was showing this morning, which showed the line shifting westward. Most of the rainfall has been focused over Oahu and Maui County, with a few hundredths of an inch recorded at most locations since this morning.

For what it's worth (and it may not be much based on what was already mentioned), hi-res model guidance suggests that shower activity will diminish later this afternoon as the current line lifts north and falls apart, then additional light to moderate showers may reorganize along another weakly convergent boundary near Kauai overnight and persist in the vicinity through at least Tuesday. For the latter part of the week, trades will try to return, but may have a hard time doing so as a nearly stationary surface trough forms and persists northwest of the state, making it hard for the high pressure to the northeast to take over the local winds. Overall, winds are expected to be light east to southeasterly. With light winds prevailing, and if diurnal heating is strong enough, land and sea breeze activity may bring interior showers during the day and partial clearing overnight for the rest of the island chain. Otherwise, isolated light showers will move in on the weak southerly flow for the west half and on the southeasterly flow for the east half that will become light east to southeasterlies across the state for the latter part of the week.

With lots of deep moisture sticking around through the forecast period, a mix of low and high clouds will stick around and it won't take much to trigger shower development. Precipitable water values (PWats) are expected to remain between 1.8 and 2 inches through midweek before dropping slightly to 1.5 to 1.8 inches for the latter half. For reference, the average PWats for this time of year is around 1.2 inches.

This weekend, an upper level trough will dig down rather close to the state from the northwest. While most of the model guidance doesn't do much with it at this point, it's worth keeping an eye on to see if it will help to enhance shower activity over portions of the state, especially with ample moisture lingering and cooler temperatures moving in aloft.

AVIATION

Stratiform rain will continue to impact the islands today, however generally VFR conditions are expected due to the light intensity of the rain. MVFR conditions are most likely at more elevated sites such as Molokai and Lanai, as well as under periodic bursts of heavier rain. Winds will generally be driven by land-sea breezes, flowing light at less than 10 kts. The forecast generally trends back toward benign trades by the midweek.

AIRMET Sierra remains in effect for mountain obscuration for Kauai and Oahu. This may be scaled back further as the rain gradually lets up heading into tomorrow.

Moderate icing is possible so long as this ongoing system remains over the islands.

MARINE

A weak surface trough remains draped across the state, leading to pockets of light winds over the central islands. Winds may be stronger tonight when enhanced near island terrain, such as southeast near the Big Island or south near Kauai, before diminishing Tuesday. The surface trough weakens and lifts out the latter half of the week. High pressure begins to take over at the surface, causing gentle to moderate easterly trades to gradually develop across the Hawaiian coastal waters by this weekend.

A small, medium-period northwest swell has diminished, with small surf persisting along north and west facing shores due to a reinforcing pulse on Tuesday. Following this, northwest swell energy declines through the rest of the week.

A new south swell arrives on Tuesday, providing a boost to surf along south facing shores through mid week before gradually subsiding into the weekend.

Surf along east facing shores will remain below seasonal average with lighter than average trade winds near and upstream of the islands forecast through next week.

HFO WATCHES/WARNINGS/ADVISORIES

None.