An approaching cold front will being enhanced showers and isolated thunderstorms to the western end of the state through Monday night. Unsettled wet conditions continue through most of next week as another front approaches from the northwest, then stalls across the western half of the state.
Satellite imagery and the latest surface analysis depicts a cold front approximately 100 miles northwest of Kauai this afternoon. Radar imagery shows scattered showers across the leeward Kauai and Oahu waters moving northeast, but generally remaining offshore. Southerly winds ahead of the front continue across the state, with broken to overcast skies over leeward portions of the smaller islands. The forecast remains on track, and continues to show the potential for heavy rain and isolated thunderstorms capable of producing flash flooding across portions of Kauai County and Oahu. A Flood Watch remains in effect for Niihau, Kauai, and Oahu from midnight tonight through 6 AM Tuesday morning.
The latest hi-res guidance shows the front reaching Kauai around midnight tonight, the moving eastward and reaching Oahu around daybreak on Sunday. The front looks to then briefly stall over East Oahu Sunday afternoon and evening, before retrograding west and stalling out in the vicinity of Kauai or Oahu Sunday night into Monday. There remains good agreement with the evolution of the upper level support associated with the system as a strong 100+ kt southwesterly jet helps to deepen the front and provide a narrow corridor of strong uplift. This in turn will result in a mature jet-front system that will support the development of a band of heavy rain and isolated thunderstorms. There still remains some uncertainty where this band of heavy rain will eventually settle Sunday night into Monday, but the western half of the state could see anywhere from 1.5 to 3 inches between now and Monday night, with locally higher amounts possible.
The upper level support is expected to lift north on Tuesday and bring the surface low with it. The surface front will also lift and weaken, although lingering moisture will remain in the area keeping some showers around the area on Tuesday. Another surface low looks to develop near the dateline on Monday, then move east through late next week. Guidance continues to show a front approaching the islands from the northwest mid to late next week, with the front elongating and stalling over the western half of the state by late next week. There is still some uncertainty with how strong this front will be, but expect additional showers and unsettled weather continue through the rest of the week.
Southerly winds have increased this afternoon. Expect elevated and gusty winds to continue especially across the western half of the state ahead of a front that is approaching Kauai. This front will bring low cigs, SHRA and a few tstms. IFR/MVFR conds possible across the western end, while a few eastern end sites will remain VFR.
AIRMET Sierra is in effect for mtn obsc for Kauai and Oahu. As conds deteriorate this may become an IFR AIRMET.
An approaching front will reach of Kauai late this evening potentially advancing as far east as Oahu by early Sunday. The Small Craft Advisory for strong SW winds in advance of the front has been extended until Monday morning due elevated seas poised to arrive during Sunday morning. Winds rapidly diminish in the wake of departing low pressure Sunday morning but again become locally fresh out of the S Monday through mid-week as another front approaches from the west. Southerlies continue through the week. Isolated thunderstorms have been observed along the cold front and will be possible within the western nearshore waters tonight into Monday.
Energy associated with the existing NNW swell is small and concentrated in the shorter periods favoring a slight downward adjustment to the surf numbers for N facing shores for this evening. Forerunners associated with a new moderate medium to long period NW swell have pinged on the NDBC offshore buoys this afternoon. This energy will build into the nearshore waters tonight into Sunday. Surf will build rapidly during the morning peaking near High Surf Advisory thresholds for N and W facing shores by Sunday afternoon. A combination of moderate NW and N swells will maintain elevated surf elevated through the first half of next week.
E shores remain tiny to small given the lack of trade winds but shorelines exposed to N swells may be slightly elevated through Wednesday. Surf along S shores will see an increase of short period wind wave chop mainly over the western islands this weekend associated with the passing front. A slight lull is expected Sunday before the next front approaches and increases the wind waves coming from the south.
Flood Watch from midnight HST tonight through late Monday night for Niihau-Kauai Leeward-Kauai Mountains-Waianae Coast-Oahu North Shore-Olomana-Central Oahu-Waianae Mountains-Kauai North- Kauai East-Kauai South-East Honolulu-Honolulu Metro-Ewa Plain- Koolau Windward-Koolau Leeward.
Small Craft Advisory until 6 AM HST Monday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters.
