The cold front near Maui has dissipated into a surface trough this morning. Windy trade winds will continue to strengthen over the state as a high pressure system builds in from the north. A deepening upper low will linger west to southwest of the Hawaiian Islands through Monday before drifting westward away from the islands by Tuesday. High pressure building in from the north will produce stronger trade winds today above warning levels in some areas. Unstable conditions from the nearby upper low, deep unstable moisture and strong winds flowing over mountain ranges will keep periods of heavy rain, thunderstorms, and flooding threats in the forecast through Monday. Heavy shower activity and flood threats will diminish from Tuesday onward as the upper low departs the pattern. Wind speeds will decrease slightly from Tuesday into Wednesday, likely falling just below advisory thresholds for the second half of the week.
Periods of heavy rain continue to threaten the Hawaiian Islands through Monday. Overnight rainfall amounts in rain favored areas ranged from 1 to 4 inches across the state. See Hawaii Rainfall Summary product (RRAHFO) for details. Terrain anchored storms along windward slopes (north and east slopes) of each island represent the highest flood threat due to the strong trade winds driving heavy rain up against the windward mountain ranges of each island. Last night these terrain anchoring storms formed rapidly along the windward slopes of the Kohala Mountains and the Hamakua Coast on the Big Island where the highest rainfall totals were observed. An area from eastern Waimea town to Waipio Valley and to Honokaa reported the highest rainfall with over 7 inches of rain falling over a three hour time period. A Flood Advisory was upgraded to a Flash Flood Warning for this Big Island event, and several land slides were reported in the area by the Hilo Police Department. A Flood Watch also remains in effect statewide through Monday.
Snow levels will remain around the 11,000 foot level through this event and a Winter Storm Warning continues for snow and blowing snow over the highest summits of Mauna Kea and Mauna Loa on the Big Island through Monday.
Strong damaging winds are an additional threat lasting at least through Monday, and possibly lasting into Tuesday. A Wind Advisory will upgrade to a High Wind Warning this morning as windy trade winds continue to strengthen throughout the day. The primary mechanism for these damaging winds will develop as strong trade winds may create breaking mountain waves that will pull down stronger winds aloft and cause damaging wind gusts to around 60 MPH along southern and western slopes of island mountain ranges. Additionally, as convective heavy showers and thunderstorms develop they will reach up into the higher levels of the atmosphere and pull down these stronger winds aloft producing wind gusts to around 60 MPH at the surface level over the next 48 hours. These winds will gradually decrease from Tuesday into Wednesday, however breezy to locally windy easterly trade winds will linger through the end of the week.
The weather pattern begins to shift from Monday night into Tuesday as the upper low lingering just southwest of the Hawaiian Islands begins to drift farther westward away from the state. Models remain in good agreement that this pattern shift will herald stabilizing trends, effectively eliminating the threats of heavy rain and thunderstorms over the islands from Tuesday onward. However, continued strong easterly trade winds through the week will continue to produce periods of wet trade winds over the islands, just at a lower intensity each day due to increasing subsidence aloft and a lowering of the temperature inversion height.
A surface trough over the state will be enhanced by an upper trough to the west. SHRA and low cigs are causing MVFR and isol IFR conds. Winds will increase significantly over the next 12 hours. Gusts in excess of 35kts are already occurring across some of the smaller islands. With increasing winds there is the potential to see even higher gusts.
AIRMET Sierra is in effect for mtn obsc for all islands.
AIRMET Tango is in effect for for mod turb across all islands and adjacent waters due to the weather system over the state. Mod turb may occur across all portions of these islands up to FL320.
Light icing is expected in cloud layer 100-FL250 from Kauai to Maui.
A trough currently over central waters, a developing low pressure several hundred miles southwest of the islands and strong high pressure building north of the front is driving these strong to gale force northeast trade winds along and north of the feature. A Small Craft Advisory (SCA) remains in effect for all Hawaiian waters due to a combination of winds and large. A Gale Warning will be in effect starting this morning through Monday afternoon for all coastal water zones for winds and seas. In addition, expect heavy showers and isolated thunderstorms through Monday. Winds are expected to ease some on Tuesday, but trade winds will remain in the strong range with some locally near gales over the windier waters and channels through the forecast period.
The current moderate west-northwest swell (295-310 degrees) will continue to gradually decline through Monday. The High Surf Advisory (HSA) has been cancelled for all north and west facing zones. Small to moderate north- northwest to northwest swells will prevail through the remainder of the week.
Large and very rough seas will begin to develop today as trade winds strengthen. East shore surf should rise above the HSA threshold tonight, with the potential for surf to reach the High Surf Warning (HSW) level Monday and Tuesday on Kauai and Oahu. Large east shore surf will slowly decline Tuesday into Wednesday but will still remain somewhat elevated through the remainder of the week. Surf along south facing shores will remain small with some small background south-southwest energy expected throughout the first half of the week. Select southern exposures exposed to the wind swell will likely see some larger waves as well.
Flood Watch through Monday afternoon for all Hawaiian Islands.
Wind Advisory until 6 AM HST early this morning for all Hawaiian Islands.
High Wind Warning until 6 PM HST Monday for all Hawaiian Islands.
Winter Storm Warning until 6 PM HST Monday for Big Island Summits above 11,000 feet elevation.
Small Craft Advisory until 6 AM HST early this morning for all Hawaiian waters.
Gale Warning until 6 PM HST Monday for all Hawaiian waters.
