A cold front advancing down the island chain this morning is bringing gusty northerly winds near and west of the boundary and showery conditions. The front is expected to stall and gradually weaken around Maui County later today through Thursday, bringing additional periods of showery weather. Rainfall chances will trend up statewide Friday through the weekend as another cold front and upper disturbance approach and move into the area. Conditions should gradually improve from west to east through the first half of next week as high pressure builds eastward over the region.
A line of showers associated with a cold front that moved through Kauai is now moving over Oahu this morning (3 AM HST). Peak rainfall accumulations over the past 6 hours ranged from 4 to near 7 inches along north- through west-facing slopes of Kauai. In addition to localized heavy rainfall accompanying the boundary, a band of strong northerly winds is occurring along and behind the front, with some of the windier locations on Oahu and Kauai reporting gusts to around 40 mph. Similar conditions are expected through the morning hours as the boundary progresses eastward into Maui County.
Guidance has initialized well with the current synoptic pattern and depicts the front stalling and lingering near Maui County by Thursday. A broad upper-level trough, with several shortwave pulses rotating through its base, will support periods of lingering showery weather along the moisture axis over the next few days, particularly over windward and mauka locations with the northeast flow in place.
Despite some remaining differences among the ensemble solutions, agreement has improved considerably compared to 24 hours ago. The majority of solutions indicate low-level flow will shift out of the southeast in a return-flow pattern as another frontal system evolves and approaches the islands over the weekend. Increasing instability aloft associated with the upper trough and an embedded shortwave, combined with deep moisture pooling northward across the islands, will support a wet pattern through the weekend. Conditions should gradually improve through the first half of next week as this system moves through, upper-level heights rise, and drier air moves in as surface high pressure builds to the north in its wake.
A cold front over Oahu will continue to advance southeastward and weaken through the morning. The front should reach Maui County later this morning before stalling out. Winds will be light and variable ahead of the front, and breezy, gusty, and northerly behind it. Most of the showers can be expected along the front with MVFR cigs/vsbys. Winds then veer northeast later today into tonight and showers turn to a more typical trade wind distribution. The bulk of the showers should be over Maui County later today with the remnants of the front.
AIRMET Tango is in effect for moderate upper level turbulence between FL310 and FL370 due to jet stream winds. AIRMET Tango is also in place for the S slopes of the mountain terrain for Kauai and Oahu due to the strong northerly winds. This AIRMET will likely be dropped later in the morning as the winds decrease. AIRMET Sierra is in place for Kauai and Oahu from the showers associated with the front and will likely be dropped later in the morning as the front moves on. AIRMET Sierra may be needed for Maui County later in the morning due to the moisture with the front.
Strong north to northeast winds and rough seas will affect the western half of the marine area this morning, as a cold front moves into Maui County. The front will then stall out across the central islands late today and tonight, with winds gradually easing and becoming more northeasterly. A Small Craft Advisory (SCA) is now in effect for the western half of the marine area through noon today. Around the Big Island, expect gentle east to southeast winds to continue on the south side of the stalled out front. A weak surface ridge will develop a couple hundred nautical miles north of Kauai on Thursday, leading to gentle to moderate easterly trade winds through Friday night. Winds will turn out of the southeast and south over the weekend as another front approaches from the northwest, while a disturbance aloft could trigger a few heavier showers and possibly thunderstorms during this time as well.
Overlapping west-northwest to north-northwest swells will produce surf slightly below High Surf Advisory (HSA) levels for exposed north and west facing shores through Friday. Gusty north to northeast winds will produce rough and choppy conditions along north facing exposures of the smaller islands today, particularly this morning. A sharp downward trend in north shore surf is expected over the weekend, followed by a potentially large northwest swell arriving Monday night and Tuesday.
East shore surf will remain below seasonal average through the week, although a brief increase is possible on Kauai and Oahu this morning due to strong post-front northerly winds. Surf along south facing shores will remain very small through the week.
Small Craft Advisory until noon today from Maui County to Kauai waters.
