textproduct: Honolulu

SYNOPSIS

Surface high pressure northwest of the Hawaiian Islands will slowly slide east over the next several days. Passing showers are possible over windward and mauka areas during this time period, mainly during the overnight to early morning hours. The next best chance for statewide rainfall should arrive Tuesday and Wednesday as increased low level moisture arrives with an old cold front drifting into the region.

DISCUSSION

Radar indicates scattered light showers across windward and mauka areas, and the open waters early this morning. Some continued uptick in coverage is expected this morning, but showers will weaken outside of windward areas this afternoon.

Mid level ridging will remain centered overhead through the middle of next week. Surface high pressure northwest of the islands today will slowly slide east to our northeast Sunday night. An upper level low will approach from the northwest Tuesday. In addition, a band of low level moisture associated with an old frontal boundary will move across the state from the east and northeast. These features will lead to an increased chance for showers midweek. Maintained very high PoPs for windward and mauka locations, but even leeward areas may see a few showers at times.

The upper low will dissipate as it finally reaches Hawaii around Thursday. Weak, broad ridging may build somewhat to our west late week and next weekend. This flow pattern may allow for more old fronts to pass through the state, but the timing of these is of low confidence at this range.

AVIATION

Trade winds will continue with brief periods of passing showers over windward and mountain areas favoring the overnight to early morning hours. Improving weather trends during the daylight hours.

AIRMET Tango remains in effect for low level moderate turbulence over and downwind of island mountains.

MARINE

High pressure north of Hawaii will drive fresh to locally strong trade winds today. A new high pressure system building north of the islands will cause trade winds to strengthen back to strong levels for most waters by tonight. Therefore, the Small Craft Advisory (SCA) remains in effect for the typical windy waters near Maui County and the Big Island today, with an expansion to cover all coastal waters tonight. Winds will diminish somewhat on Sunday as the high shifts quickly to the northeast, but a new north swell will push seas above 10 feet for exposed waters which will prompt an extension of the SCA for at least some zones beyond just the typically windy ones (likely all windward zones). Next week will see continuing fresh to strong trades with some minor fluctuations each day.

A moderate, medium-period north-northwest swell will continue to decline today. A new small, long-period north-northwest swell will help support small surf through the day before the arrival of a more significant north swell late Saturday night. This moderate, long- period north swell will push surf to near advisory levels on Sunday for north and west-facing shores. This swell, at around 350 degrees, looks to peak around 6 feet, 15 seconds Sunday afternoon and evening, which may lead to surges into north-facing harbors. Surf to at least moderate levels, along with harbor surge potential, will last into Monday before the swell really begins to fade on Tuesday. A small to moderate northwest swell is then possible by next weekend.

Surf along east-facing shores will remain rough and choppy due to the fresh trade winds and increase tonight into Sunday with strengthening trades. South shore surf will stay tiny to small for the next few days, then a small long-period swell could boost surf heights towards the end of next week.

FIRE WEATHER

Fire weather conditions will remain below critical, limited by wind speeds for most areas and by higher minimum humidity levels for the higher elevation zones that reach wind thresholds. Wind speeds will increase into the moderate to breezy levels later today, lasting into early next week. Temperature inversion heights near Maui and the Big Island will range from 6,500 to 7,500 feet elevation today.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory from 6 PM this evening to 6 AM HST Sunday for Big Island Windward Waters-Kaiwi Channel-Kauai Channel-Kauai Leeward Waters-Kauai Northwest Waters-Kauai Windward Waters-Maui County Leeward Waters-Maui County Windward Waters-Oahu Leeward Waters-Oahu Windward Waters.

Small Craft Advisory until 6 AM HST Sunday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Maalaea Bay-Pailolo Channel.