| Current Conditions | ||
| Temp |  | 5.1 C |
| RH | | 21 % |
| Wind | | W 8 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 876 FXHW60 PHFO 231356 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 356 AM HST Wed May 23 2018 .SYNOPSIS... Refreshing trade winds will continue into the upcoming Memorial Day weekend as a high pressure system passes north of the area. The trades will be particularly breezy through Thursday night before weakening on Friday and Saturday. && .DISCUSSION... A new surface high pressure system with a central pressure of 1031 mb is currently 915 miles N of Kauai. It will be moving slowly E, passing N of the islands during the next 24 hours. In doing so, rather breezy trades are in store for the islands through Thursday night, and may be Friday. Trades are in the forecast for Memorial Day, but is subject to change. The high will be some 1600 miles NE of the islands by Saturday, far away where the trades trend weaker to moderate to locally strong, with the strong pertaining to Maui and the Big Island. The trades may trend even lighter to light to moderate speeds by Monday of next week. A dissipating front is located 300 miles N of Kauai. It is not expected to reach the islands. However, scattered, fragmented pieces of shower-bearing clouds, embedded in the trade flow, will affect the windward and mountain areas of about all the islands into the foreseeable future. Due to the breezy trades, expect a few of these showers to venture downwind into the lee areas of the smaller islands. Relatively light rainfall amounts are expected with these showers. The air mass is quite stable over the islands, with a pretty strong inversion between 6500 feet over Lihue, and 8500 feet over Hilo. This air mass is forecast to last through the Friday before weakening over the weekend, where the inversion rises to 10k feet state wide. The GFS is ushering in an area of high precipitable water (PW) on Monday with values around 1.65 inches. Most of the PW is due to a dense layer of mid and high layered clouds in association with an upper level trough just west of Kauai. There are some uncertainties and differences between the ECMWF and GFS in the handling of the upper trough late in the weekend and Monday. The GFS solution is faster than the EC with the upper trough over Kauai Monday evening, while the EC has the trough west of Kauai. The earlier 00z GFS run had low level ESE winds over most of the area. The 12z run is quite different with moderate to strong trades. The ECMWF shows an inverted trough over Maui County. In due course, the model will iron out these differences. At this point, as far as Memorial Day is concern, we have sided with the GFS solution, that is for mainly moderate trades. But, it should be cautioned that this is subject to change. && .AVIATION... High pressure north of the state will maintain locally breezy trade winds over the next few days. The early morning soundings from PHTO and PHLI show a strong low level inversion between 6-8 kft. The combination of the breezy trade winds and stable atmosphere will create conditions for more wide spread low level turbulence and and AIRMET TANGO is posted over and immediately south through west of the mountains. Low level moisture embedded in the trades will focus clouds and isolated to scattered showers along the windward and mountain slopes. Some passing showers may introduce periods of MVFR CIGS/VIS. Otherwise, expect predominately VFR conditions. Periodic explosive eruptions at Kilauea/Halemaumau crater continue to produce periods of volcanic ash, with the plume of emissions predominately rising to the inversion level and extending to the southwest over Kau district on the Big Island. MVFR VIS can be expected in this area. Volcanic ash SIGMET TANGO series remains in place at this time. && .MARINE... High pressure passing by to the north of the state will keep a breezy trade wind flow in place across most of the coastal waters through Thursday night before easing off slightly on Friday. The trades are expected to trend down a little more over the weekend as an approaching front shifts the high northeastward and further away from the island chain. A Small Craft Advisory (SCA) is now in effect for most marine zones through tonight, and all waters east of the Kauai Channel with the exception of the windward Big Island waters through Thursday night. SCA conditions will likely continue into the weekend for the typically windy waters around Maui and the Big Island. No significant swells are expected, with surf remaining below advisory levels into next week. A small, long-period south- southwest swell will slowly build today, then continue into the weekend. A small north-northwest swell will peak today then slowly diminish through Thursday. Another small northwest swell may give surf a slight bump along north facing shores over the weekend. Breezy trade winds will deliver choppy short-period waves to east facing shores into the weekend. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Friday for Maalaea Bay, Pailolo and Alenuihaha channels, and waters south of the Big Island. Small Craft Advisory until 6 AM HST Friday for Oahu windward and leeward waters, Kaiwi Channel, and Maui County windward Waters and leeward Waters. Small Craft Advisory until 6 AM HST Thursday for Kauai Northwest waters and Kauai Channel. && $$ Lau/Eaton/Jelsema Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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