textproduct: Honolulu

SYNOPSIS

Changes are on the way as two fronts will move through the state this week. The first will bring showers and northerly winds tonight into early Monday. Showers should linger Tuesday as the remains of the front move back west over the state. The second front arrives Wednesday night into Thursday, bringing another round of showers and even stronger winds. Pre-frontal winds Wednesday afternoon could be quite gusty. The week should end cool and fairly dry with trades re-established.

DISCUSSION

A few showers have popped up this afternoon on Oahu, but rainfall amounts have been limited to just a few hundredths as the atmosphere remains relatively stable. Otherwise, skies were partly cloudy on most islands and winds were light and out of the south through southwest at most locations.

A cold front is moving toward Kauai County this afternoon, and will move through much the state overnight and early Monday before stalling out near the Big Island late Monday. Moderate to occasionally heavy showers will accompany the front, and winds will become northerly after passage. Tuesday morning low temperatures will be around 5 degrees below normal due to the dry air coming in with the front. By Tuesday afternoon, winds will swing rapidly around to easterly and then southeasterly as the front begins to move back west over the state. Additional showers will form as this occurs.

Wednesday, a new front will approach from the northwest. As the mass field adjusts to an incoming upper level trough, we will have a period of strong south to southwest surface winds over the smaller islands. Gusts of 25 to 35 mph are expected Wednesday afternoon, especially over higher terrain and just downwind (what is normally windward will briefly become leeward during this period of southwest surface winds). Headlines for wind may be needed as we get closer in time. The front is forecast to get to Kauai County around sunset, Oahu in the evening, Maui County before sunrise, and Big Island by noon Thursday. This will bring another round of showers, some possibly strong. Fast movement through the state should limit the risk of flooding.

Friday and Saturday will be cool as relatively dry air moves in behind this second front. Trades will build back in, pushing the remnants of the front south of the state. Showers should be limited as this prevents the moisture from passing back over the state as with the first front earlier in the week.

AVIATION

Light background winds have resulted in daytime sea breezes across the island chain again today, increasing cloud cover and producing a few showers over the islands (especially Oahu).

A cold front that is currently to our northwest will arrive across the western end of the state tonight and then progress down the island chain through Monday. Showers are expected along the frontal boundary, with prevailing MVFR conditions as the front moves through. Behind the front, breezy northerly winds will fill in, along with drier conditions.

There are no AIRMETs currently in effect. However, AIRMET Sierra for mountain obscuration will likely be needed this evening and tonight due to increasing clouds and showers, starting on Kauai.

MARINE

A strong cold front moves down the island chain from west to east, stalling out near the Big Island by Monday night. By Wednesday an even stronger cold front will quickly move through the islands, spreading strong to near gale force winds across the northwestern coastal waters late next week into Thursday. A Small Craft Advisory remains in effect for coastal waters exposed to the large northwest swell, these elevated combined seas around 10 feet are forecast to linger over waters and channels exposed to this northwest swell energy.

A High Surf Advisory (HSA) is in effect through Monday morning for north and west facing shores exposed to the large northwest swell energy. This swell will hold above HSA thresholds into Monday as yet another much larger overlapping northwest (320-330 degree) swell swiftly builds surf to High Surf Warning (HSW) levels from Monday through Tuesday. We will likely issue an HSW on Monday to cover this next warning level surf event. Yet another XL northwest (320-330 degree) swell will build into the region by Thursday, potentially producing another round of warning level surf along north and west facing shores lasting through Friday. This northwest swell energy will diminish into next weekend.

Surf along east facing shores will remain small through the first half of this week due to a continued disruption in the trade wind flow. Surf heights will remain very small along south facing shores through the forecast period.

HFO WATCHES/WARNINGS/ADVISORIES

High Surf Advisory until 6 AM HST Monday for Niihau-Waianae Coast-Oahu North Shore-Maui Windward West-Kauai North-Kauai East- Molokai Windward-Molokai North-Molokai West-Maui Central Valley North-Windward Haleakala.

Small Craft Advisory until 6 PM HST this evening 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.