In the large scale, two surface Kona low pressure systems continue to move slowly northeastward through the northern Hawaii Islands through the weekend, producing additional periods of moderate to heavy rain, thunderstorms, and elevated threats for flash flooding statewide. A combination of low level forcing and passing upper level troughs will drive smaller scale heavy rain bands and thunderstorms. These smaller scale cloud bands are less predictable and will produce the heaviest rainfall rates in the 2 to 4 inches per hour range. Additional weather threats include strengthening south to southwest Kona winds today that may produce down sloping wind gusts in the 30 to 45 MPH range along steep north and east slopes of island mountain ranges lasting through tonight. Improving weather trends will develop from west to east on Monday as we transition to a wet trade wind weather pattern lasting through the end of next week.
This mornings satellite imagery showers a long lived smaller scale low level convergence band slowly drifting eastward through Maui County. The heaviest showers and thunderstorms are currently developing along this convergence band within 50 miles north and south of Molokai early this morning. This band will continue the be the primary driver of heavy rain over Maui County today as it slowly drifts eastward into Maui later this morning. For Oahu, a broad band of enhanced clouds are moving towards Oahu and are consolidating along a new low level smaller scale convergence band. Showers are already increasing across the island with deeper. cloud heights rising into the 25,000 to 30,000 foot range based on satellite cloud top temperatures and may lead increasing moderate to heavy showers over Oahu. Enhanced showers are also shown on radar imagery developing just upstream of Kauai and the Big Island. We continue to watch this fluid situation closely as the heaviest rainfall impacts will evolve on an hour by hour timeline. Stay vigilant this weekend.
Focusing on the larger scale for a moment, we continue to see two surface lows within the larger Kona low structure drifting towards the northeast passing just north of the island of Kauai. The highest upper level forcing from this Kona low will develop over Oahu and the islands of Maui County into Sunday. The Big Island will likely see additional large scale forcing by early Sunday morning into Monday with this system.
By Monday, the pattern begins to change for the western islands as cool northeasterly trades blow into Kauai and Oahu. Returning trade winds will signal improving weather trends as the deep moisture and unstable atmosphere will be driven towards the south, away from the islands. By Tuesday, deep unstable moisture will clear up over Maui County and the Big Island of Hawaii with improving weather trends. Upper level troughing will linger across the Hawaii region next week. However, heavier showers will diminish as the weather pattern shifts back to a more typical wet trade wind weather pattern. Passing light to moderate showers will favor the typical windward and mountain areas with this easterly trade wind pattern lasting through next weekend.
A band of showers with embedded thunderstorms continues to bear down over Maui County early this morning. This ongoing Kona low will support further shower activity across Oahu and Maui County through the period, with rain chances potentially spreading to Kauai and the Big Island as well, however confidence is lower for those latter two areas. Winds will remain primarily south, potentially veering more southwest as the day progresses. Expect MVFR down to locally LIFR conditions under showers.
AIRMET Sierra for mountain obscuration remains in effect for Oahu, Molokai, and Maui, and is expected to continue through the period. Lanai was converted to an IFR category as low cigs near the surface continue to prevail there, and may persist so long as we stay under this Kona low pattern.
AIRMET Tango also remains in effect for moderate turbulence downwind of terrain for Oahu and Maui County below 090, and is expected to continue through at least the day Saturday as gusty south to southwest winds are observed across both islands.
Light icing in layer 140-FL260 will also persist so long as high clouds envelop the islands due to this ongoing Kona low.
Light to moderate S winds expected as the surface low pressure west of Kauai deepens. Moderate to locally strong S/SW prevails today, and periods of heavy showers and a few thunderstorms are expected. The low will lift north on Sunday allowing moderate N winds to develop around Kauai which will then veer to NE and spread south. Due to wave heights around Niihau, Kauai and Oahu in the 8-12 foot range a Small Craft Advisory is in effect for those waters until 6AM Sunday.
A northerly swell is building in and will create large surf for north facing shores of Niihau, Kauai and Oahu that will peak Saturday afternoon and then slowly decline Saturday night. As such A High Surf Advisory (HSA) is in effect for north facing shores for Niihau, Kauai and Oahu until 6AM Sunday. The south swell is slowly declining and will continue that trend through the weekend into early next week. Surf along E shores is elevated due to the north swell and will be near HSA thresholds. This swell will slowly diminish through the weekend. Smaller surf is expected along south facing shores through the remainder of the week.
Flood Watch through Sunday afternoon for all Hawaiian Islands.
High Surf Advisory until 6 AM HST Sunday for north facing shores of Niihau, Kauai and Oahu.
Winter Storm Watch from this evening through Sunday afternoon for Big Island Summits.
Small Craft Advisory until 6 AM HST Sunday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel- Oahu Windward Waters-Kaiwi Channel.
