textproduct: Honolulu

SYNOPSIS

A weak cold front, currently moving towards Oahu through the Kauai Channel this morning, will continue to spread clouds and enhanced showers to the other islands through Saturday as the frontal cloud band slowly drifts eastward down the island chain. Moderate to breezy north to northeast winds will blow in as the front passes each island. Another stronger front is forecast to approach late Sunday, bringing breezy southwesterly winds into Monday. More significant showers will develop along this next frontal band as these clouds and showers march eastward down the island chain from Monday to Tuesday, before stalling out and diminishing near the Big Island on Wednesday. Expect cool and dry, breezy northwesterly to northerly winds to blow into the region after the front passes each island.

DISCUSSION

This mornings big picture satellite imagery shows the leading edge of the front passing eastward through the Kauai Channel towards Oahu. A few high clouds will stream in from a polar jet stream farther to the north. Expect cloudy skies and periods of showers to continue over Kauai and Niihau today, Oahu will see increasing shower trends this morning as the frontal cloud band rolls into the Gathering Place.

Clouds and showers along the frontal band will reach Molokai around noon HST, Lanai and Maui around 2 PM HST this afternoon, and the Big Island just after midnight on Saturday morning. Rainfall will favor north and east slopes of each island with decreasing rainfall amounts along the front as it passes through each set of island terrain. Cool northerly winds with decreasing shower trends will blow in behind the front, indicating the cold front has passed through your local area.

A high pressure cell on an eastward track will pass just north of the Hawaiian Islands this weekend, producing a brief period of fairly stable easterly trade winds lasting into Sunday morning for most islands. The next cold front will then approach the islands from the northwest, cold air and troughing aloft will break down the ridge near the islands producing southwesterly winds from Sunday afternoon onward. A few passing showers may develop in this southwesterly wind pattern, favoring south and west slopes of each island into Monday.

The medium range model solutions show this cold front moving into Niihau and Kauai around noon HST Monday with similar trends of increasing showers along the frontal cloud band. This front appears slightly stronger than the previous front and more rainfall will likely develop with this next system. The latest timing on this next front shows the frontal cloud band spreading showers into Oahu by Monday evening, to the islands in Maui County from Monday night into Tuesday morning, and finally stalling near the Big Island from Tuesday afternoon into Wednesday. Storm total rainfall amounts of 0.25 to 0.50 inch with locally higher amounts are possible as the front passes each island. Cool, dry and stable northwesterly to northerly winds will once again blow in behind the front.

This Hana Hou weather pattern continues into the end of next week, another brief period of easterly trades as a high center passes north of the state, followed by southwesterly winds ahead of yet another, even stronger cold front approaching the islands bringing potentially heavy rain showers and thunderstorms for the end of next week. Stay tuned as the weather forecast with this third front may turn threatening and island by island impacts will likely evolve over time.

AVIATION

An advancing weak frontal boundary moving southward will make its way across the Hawaiian Islands this morning, bringing periods of increased cloud coverage and shower activity. Expect MVFR conditions along the front as it advances. Winds across the islands will remain generally light and variable ahead of the front, but will shift more northern as the front passes, veering more northeasterly later this afternoon into the evening hours.

AIRMET Sierra remains in affect for tempo mountain obscuration above 2000 feet across Kauai and Oahu, but may need to be expanded to Molokai, Maui, and Lanai as the front continues to advance south.

MARINE

A front moving over the western coastal waters early this morning will continue moving southeast down the island chain today. Light and variable winds ahead of the front will be replaced by moderate to fresh north to northeasterly winds in its wake. Light easterly trade winds will briefly return to Hawaiian waters Saturday night and early Sunday, with moderate to locally strong southwesterly winds developing ahead of the next cold frontal system approaching from the northwest late Sunday through Monday. This next cold front will move down the island chain from late Monday night through Tuesday, increasing chances for showers. Fresh to locally strong northwesterly winds will build in behind the front as it passes.

Nearshore buoys at Hanalei and Waimea show that a moderate to large northwest swell is moving through the islands, pushing surf along north and west facing shores well into advisory levels early this morning. However, a bigger and longer period northwest (300-320 degree) overlapping swell is expected to fill in during the day today. This second swell is expected to peak this afternoon and evening, pushing surf heights above warning levels into Saturday for select north and west facing shores. With this morning's forecast updates, a High Surf Warning (HSW) has been issued for north and west facing shores of Niihau, Kauai, Oahu, and Molokai. A High Surf Advisory (HSA) also remains in effect for north facing shores of Maui and west facing shores of the Big Island. In addition, the Small Craft Advisory (SCA) has been expanded to include all windward waters and channels exposed to the northwest swells, where seas are expected to reach into the 10 to 14 foot range. These large northwest swells will decline from Saturday into early next week. Looking ahead, an extra large northwest (310-330 degree) swell may fill in from Tuesday through Wednesday of next week.

A Coastal Flood Statement remains in effect for low-lying shoreline and roadways due to the combination of large surf and higher than predicted water through Monday afternoon.

Surf along east-facing shores will remain small due to the lack of trades locally and upstream of the state. Surf along south- facing shores will also remain small over the next several days.

HFO WATCHES/WARNINGS/ADVISORIES

High Surf Warning until 6 PM HST Saturday for north and west facing shores of Niihau, Kauai, Oahu and Molokai.

High Surf Advisory until 6 PM HST Saturday for north facing shores of Maui and west facing shores of the Big Island.

Small Craft Advisory until 6 PM HST Saturday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel- Oahu Windward Waters-Kaiwi Channel-Maui County Windward Waters- Alenuihaha Channel-Big Island Windward Waters.