Trades will remain locally strong today as Tropical Storm Moke moves westward, several hundred miles south of the islands. This system will begin to deliver periods of rainfall to Big Island this morning, Maui County by this afternoon, then Oahu and Kauai by late this evening. The heaviest and most widespread rainfall is forecast along the windward and southeast slopes of Big Island. A Flood Watch remains in effect for Big Island through Monday night. A Wind Advisory is in effect for parts of Big Island and Maui County through 6 PM HST this evening. Drier trade wind weather returns Tuesday.
Latest IR satellite loop shows deep convection from Tropical Storm Moke flaring up roughly 200 miles south southeast of Hilo. Low level clouds and moisture on the northern periphery of the cyclone can also be seen racing westward towards Big Island at a steady clip. Radar is picking on these bands and depicts scattered light to embedded moderate shower activity. Radar estimated rain rates remain unimpressive though, mainly below a tenth of an inch an hour. By early afternoon, the high resolution WRF-ARW, WRF-FV3, and namNest model guidance all indicate a rather stark increase in rainfall coverage and intensity along eastern portions of Big Island. It will not take a significant amount of rain to cause flash flooding due to saturated grounds from recent heavy rain from TC Lala. Thus, a Flood Watch will remain in effect for Big Island through Monday afternoon. Rainfall amounts for the event appear in good order, as NHC's track for Tropical Storm Moke barely budged from the previous advisory package. Storm total forecast for windward and southeast Big Island remains at 5 to 10 inches with locally up to 15 inches, 3 to 6 inches for eastern Maui, and generally 1 to 2 inches elsewhere across the island chain.
Locally strong trade winds persisted overnight as Hawaii remained sandwiched between low pressure of Tropical Storm Moke south of the state and a 1025 mb surface high to the northeast. A Wind Advisory remains in effect through this evening for portions of Maui, Molokai, Lanai, Kahoolawe, and Big Island. Strongest sustained winds will continue to occur over mountain ridges, gaps and where winds blow downslope off higher terrain. Observed speeds in these areas have generally been sustained 25 to 35 mph with gusts up to 55 mph. Winds across the ridge tops of the Ko'olau and Waianae mountain ranges may near advisory criteria later today as trade wind showers and/or deeper moisture bands from the northern periphery of Moke begin to arrive. Those zones will be left out of the advisory for now, but may have to be included if the stronger winds expand further west. Trade winds across all islands should begin to ease back to moderate by tonight.
Tuesday through the end of next week, drier air will move in from the east, and typical trade winds/showers should return.
Tropical Storm Moke located a couple hundred miles south of the Big Island continues on its west-northwestward track. Rain bands from the tropical storm will impact windward Big Island today, which will bring MVFR and periods of IFR conditions to the area.
Trade winds are expected to be moderate to locally strong statewide. Outside of windward Big Island, showers embedded within the trade wind flow will primarily impact windward and mountain areas, bringing periods of MVFR conditions. Otherwise, VFR will prevail.
AIRMET Tango is in effect for low level turbulence downwind of terrain due to the strengthened trade winds. AIRMET Sierra is in effect for mountain obscurations over windward Big Island, and will likely remain through today. An AIRMET for IFR conditions over portions of windward Big Island is also a possibility later today.
TC SIGMET series XRAY covers Tropical Storm Moke and its convection.
Northeast winds have strengthened across the Hawaiian Island coastal waters, mainly around windward Big Island, as a result of Tropical Storm (TS) Moke passing west across the far southern offshore waters. At 3 AM HST, Moke's low level center of circulation was approximately located 225 nautical miles south southeast of South Point, Big Island. A Tropical Storm Warning is in effect for the offshore waters. Intense convection associated with this storm is flaring up north of its center and will impact the southeastern offshore waters generally south of 18N today. An all-water Small Craft Advisory (SCA) is in effect to account for fresh to locally strong trades between surface high pressure located far northeast of the islands and TS Moke. Higher winds and short period wind wave swell generated by TS Moke may push significant sea heights to 10 feet or slightly higher across Big Island windward waters today.
East-facing shore surf will build today in response to strengthening trades. Surf along east and south-facing shores will be impacted by a short period east southeast swell generated by TS Moke as well as northeast wind wave swell as a result of these stronger trades. As Moke passes by to the south today and Monday a mounting southeast swell will veer and become south to southwest. This small, short period captured easterly fetch from TS Moke may push Big Island east surf to near advisory levels later today.
Surf along most south-facing shores will be slightly below summer norms but still remain somewhat elevated due to a lingering small, long period south southwest swell. A three to four foot, medium to long period south swell is expected to arrive Monday and Tuesday which will maintain these near summertime heights.
Small, medium to long period west to north swell originating from Hurricane Lala is passing around north and west-facing coasts today.
Wind Advisory until 6 PM HST this evening for Lanai Mauka- Kahoolawe-Maui Leeward West-Kohala-Big Island Interior-Molokai Southeast-Molokai North-Molokai West-Molokai Leeward South-Lanai Windward-Lanai Leeward-Maui Central Valley North-Maui Central Valley South-Windward Haleakala-South Haleakala-Big Island South- Big Island Southeast-Big Island North.
Flood Watch through Monday afternoon for Big Island-
Small Craft Advisory until 6 PM HST this evening for all Hawaiian waters-
