textproduct: Honolulu

SYNOPSIS

A high pressure ridge just north of the Hawaiian Islands will continue to weaken in advance of a cold front approaching the islands from the northwest. Moderate trade winds will weaken and transition to light southeasterly to southerly winds across the region. The cold front continues to move into the western half of the state from Wednesday to Thursday. Expect cloudy skies and showers along the frontal band as it moves over each island with moderate to breezy cool northerly winds blowing in behind the frontal boundary. Light east to southeast winds will continue through the rest of the week as yet another cold front moves into the Hawaii region next weekend.

DISCUSSION

Looking at this mornings satellite imagery we see a fairly stable pattern under the influence of a weak upper level ridge. A large band of cirrus clouds associated with an approaching cold front is currently far northwest of Hawaii passing through Midway Atoll this morning. This cold front will bring increasing clouds and showers to the western Hawaiian Islands from late Wednesday through Thursday. One wrinkle in this pattern is the presence of a weak upper low shown on water vapor satellite imagery just east of the Big Island. Expect one more day of easterly trade winds with hybrid onshore sea breezes during the daylight hours along western terrain sheltered slopes of each island. Expect brief passing showers will remain in the short range forecast today, favoring windward and mountain areas. Trade winds will diminish on Tuesday with lighter southeasterly to southerly winds developing.

By Tuesday the approaching cold front will continue to break down and drive the large scale ridge directly over the islands, producing light southeasterly to southerly winds across the Hawaii region. A combination of increasing stable subsidence and southeasterly cloud steering winds will produce fairly dry conditions across the region through Tuesday night.

From Wednesday afternoon through Wednesday night the cold front will drift over the western islands of Kauai and Niihau, reaching the islands of Oahu and Molokai by Thursday morning. Expect increasing clouds and numerous showers along the frontal cloud band as it drifts through each island. Moderate to breezy cool northerly winds will blow in as the front passes through each island. The latest consensus of models shows the forward motion of the frontal cloud band stalling out over the islands in Maui County from Thursday night into Friday morning, then the band will diminish and lift northward as high pressure builds in to the north of the state.

Friday through Saturday, large scale winds will remain light and variable during this time period as a weak high pressure system, sandwiched between two cold frontal systems passes just north of the region. The next weak cold frontal system will approach the state from the northwest late Saturday into Sunday. The latest long range model guidance shows large inconsistencies on when or if this frontal cloud band will bring another round of rain showers to the western islands. For now the western islands of Kauai and Niihau seem to hold the best chances for a Hana Hou (encore) rainfall event, possibly starting by Saturday night. Stay tuned for updates to next weekends weather conditions, as the forecast for the western Hawaiian Islands will likely evolve over time.

AVIATION

Brief passing showers are possible today, mainly over island windward and mountain areas. VFR conditions will prevail outside of showers.

AIRMET Tango remains in effect for moderate upper level turbulence across the island chain. This area of turbulence associated with an upper level subtropical jet stream will move southeast today, with this moderate turbulence area decreasing by this afternoon.

MARINE

An area of high pressure will remain north of the Hawaii region, producing gentle to moderate easterly winds through today, then decrease and veer more southeasterly to southerly Tuesday to Wednesday as another cold front moves into the region from the northwest. This front may move into the western Hawaiian islands late Wednesday into Thursday, then diminish by Friday.

The current medium-period north-northwest (340-350 degree) swell will continue to slowly fade today, bringing surf back down to below average levels for this time of year. The next two long to medium-period overlapping northwest (310-320 degree) swells will arrive on today, boosting surf along north and west facing shores and possibly reaching advisory levels by Wednesday.

Choppy east shore surf will remain small, then decline further over the next few days as trades gradually ease. Expect minimal background energy for south facing shores, keeping south shore surf heights just above flat levels.

FIRE WEATHER

Conditions remain below critical fire thresholds through the week as winds remain light and RH elevated. Temperature inversion heights over Maui and the Big Island will range from 5,500 to 6,500 feet today.

HFO WATCHES/WARNINGS/ADVISORIES

None.