Periods of moderate to heavy rain continue over Leeward Big Island and Maui while conditions improve elsewhere. There is a threat for heavy rain during the latter half of this week as low pressure develops west of the islands.
Moisture embedded within deep layer SW flow extends well upstream of the Big Island and will continue to deliver waves of rainfall through at least Monday night and potentially Tuesday. However, the lack of large scale forcing during this time will likely result in a trend toward lower intensity rainfall compared to what was observed yesterday or even today. At the same time, the weakening background wind field may allow the overnight mountain breeze to more effectively focus stronger convection offshore at night. Rather nondescript surface pressure and wind fields takes shape during Tuesday which should finally bring an end to the steady stream of rainfall. At this time, the Flood Watch will remain in effect for the Big Island and Maui, though confidence in the moisture band lifting sufficiently far north to impact Maui again is low at this time. The Wind Advisory will end with issuance of the afternoon forecast package, and the High Wind Warning for Haleakala and the Big Island summits will be extended through tonight.
Attention then turns to mid to late week when the remnant frontal band reactivates in response to renewed mid/upper forcing followed by potential development of low pressure west of the islands during the second half of the week. The first upper wave arrives late Wednesday. Mid- level flow will still be southwesterly at this time, though it is uncertain whether boundary layer flow will will be in a state of weak trades of out of the south. In any case, an uptick in showers is anticipated over the islands by Wednesday night. Surface pressure falls will already be taking place upstream of the islands during this time as a trailing upper wave approaches the islands from the northwest. Model consensus previously broke down at this point with the GFS indicating a flatter and more progressive surface low while the EC indicated a deeper and slower moving low. The most recent run of the GFS has made a strong move toward the EC increasing confidence that organized low pressure will develop over or near the islands by late this week. Moderate to heavy rain then potentially develops over the islands as early as Friday and would continue into the weekend.
Showers continue over the Big Island today, and a thin band of moisture currently positioned over Molokai is moving down the island chain, providing periods of light rain. Expect showers to continue for the Big Island, providing MVFR to isolated and brief IFR conditions. Winds have weakened over the western half of the state, and remained out of the SW today, but may veer WSW later tonight. Breezy S-SW winds are still expected for Maui and leeward Big Island this evening, before weakening overnight and into tomorrow.
AIRMET Sierra is in effect for mtn obsc for all islands except Kauai. Oahu will likely be clear of mtn obsc this evening. Later tonight, it is possible for islands from Molokai to Maui to see improved conditions once the moisture band passes. Big Island will likely remain in this AIRMET through tonight.
AIRMET Tango remains in effect for mod mid-upper level turb between 130 and FL330. It is is also in effect for turb downwind N thru E of terrain statewide. The mid-upper level turb will likely continue through tonight, and the turbulence downwind of terrain will likely be limited to the eastern half of the state tonight.
Light icing is possible between 130 and FL260 as mid-high clouds continue moving through the islands.
The Kona storm that has impacted the region over the past few days will weaken as it moves northeast and away from the area, with conditions improving over the coastal waters. Latest hi-res guidance shows that locally strong winds may linger over portions of the central and eastern waters tonight. Additionally, buoy observations show that seas remain elevated, with Barber's Point and Hanalei still reporting 10ft and 12ft significant wave heights this afternoon, respectively. Therefore, the Small Craft Advisory (SCA) that was previously in effect has been extended in time through tonight to capture the seas for the western waters and locally breezy winds in the central and eastern waters (with the exception of the Southeast Big Island zone where the SCA has been cancelled). By early Monday, both winds and seas are expected to fall below advisory criteria. Winds will then remain light and variable through mid-week. Ridging is forecast to strengthen north of the islands late in the week, which should bring a return of moderate to fresh trade winds.
Large, rough surf along south-facing shores that has been observed over the past few days will trend lower tonight and Monday as wind speeds subside. A new long-period south swell will arrive late Monday night and Tuesday, giving an extended boost to south shore surf through late this week.
A moderate sized, short-period west-northwest swell will continue to affect north and west facing shores through Monday, but surf will remain below advisory levels. The one exception is for west facing shores of the Big Island, where a High Surf Advisory remains in effect through 6 AM HST. This short-period swell will lower Monday night and Tuesday, while a new medium-period north- northwest swell fills in. This north-northwest swell could bring surf up to advisory levels Tuesday night and Wednesday, with the swell then shifting more northerly and lowering below advisory levels Thursday into next weekend.
Surf along east facing shores will remain well below normal levels through the middle of the week, before trending upward Thursday into next weekend as trade winds return over and upstream of the islands.
Flood Watch through late tonight for Lanai Mauka-Kahoolawe-Maui Windward West-Maui Leeward West-Haleakala Summit-Kona-Kohala-Big Island Interior-Molokai-Lanai Windward-Lanai Leeward-Lanai South- Maui Central Valley North-Maui Central Valley South-Windward Haleakala-Kipahulu-South Maui/Upcountry-South Haleakala-Big Island South-Big Island Southeast-Big Island East-Big Island North.
High Wind Warning until 6 AM HST Monday for Haleakala Summit-Big Island Summits.
High Surf Advisory until 6 AM HST Monday for Kona-Kohala.
Small Craft Advisory until 6 AM HST Monday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel- Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-Maui County Leeward Waters-Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters- Big Island Leeward Waters.
