Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/22/16


Area Forecast Discussion
National Weather Service Honolulu HI
349 PM HST Wed Dec 21 2016 .SYNOPSIS... Trade wind weather will prevail through the week, with showers favoring windward and mauka areas, especially during nights and mornings. Although wind speeds may ease briefly on Friday, locally breezy conditions will prevail through the weekend, and stronger winds are expected early next week. && .DISCUSSION... A 1028 mb surface high will remain parked about 1300 miles northeast of the state tonight. The pressure gradient to the south of the high remains tightest over the southern end of the island chain, where trade winds will be slightly stronger through Thursday. The high will be weakened and pushed southward by a passing north Pacific front late Thursday and Friday, causing trades to decrease a notch and veer out of the east or possibly east-southeast across Kauai and Oahu. Another area of high pressure will build far north of the state this weekend, causing the trades to strengthen. During peak strength on late Sunday through Monday, locally windy conditions will be possible. A rather stable trade wind flow will focus clouds and showers over windward slopes through the week. Aside from a few areas of high clouds, a weak upper level low overhead will have little impact on island weather and will gradually dissipate during the next 24 hours. A somewhat strong mid level ridge is creating the stable conditions over the state, with recent aircraft data showing a well-defined inversion in the 3000 to 6000 foot range. Random pockets of moisture moving along the trade wind flow contain cumulus clouds topping out around 8000 ft, and as these areas move ashore, they will produce modest showers over mainly windward slopes. With a vast field of these rather shallow shower-bearing clouds extending 1000 miles east of the islands and mid level ridging holding, expect only small variations in the rainfall pattern this week. && .AVIATION... AIRMET TANGO for low level turbulence over and immediately south through west of the mountains remains in place as high pressure northeast of the state continues to deliver breezy trade winds to the area. The afternoon soundings show the inversion at PHLI still down around 3 kft, and AMDAR report in and out of Lihue confirm this. The PHTO sounding shows the inversion a bit higher, near 7-8 kft. However, the balloon likely went through a shower that pushed onto shore earlier. AMDAR soundings in and out of Kona this afternoon show the inversion between 5-6 kft. Model guidance continues to show the inversion lifting a couple thousand feet over the next day, bringing it up to near 5-6 kft across the state. Low clouds and showers riding in on the trades will favor the windward and mountain areas. Some showers will produce brief periods of MVFR as they pass. Widespread mountain obscurations are not expected, with the Big Island being the only likely culprit later tonight as showers enhance under diurnal trends. && .MARINE... The east facing shores of Maui and the Big Island remain included in the High Surf Advisory due to buoy observations showing swell with just enough energy to produce high surf conditions. The Small Craft Advisory remains in effect for most waters through tonight and for windward waters and the typically windy waters around the Big Island and Maui on Thursday. This advisory is due to a combination of a long- period north- northwest swell, trade wind swell and strong trade winds over the channels and typically windier locations. The north- northwest swell will hold through tonight before gradually easing Thursday and Friday. Surf heights will respond at the exposed shores and reach the advisory level (15 ft) during this time. As a result, the High Surf Advisory remains up for the exposed north and west facing shores through tonight. Surf associated with the strong trades locally and background trade wind swell should remain just below the advisory threshold of eight feet for the eastern facing shores west of Maui through Thursday before trending down as the trades weaken temporarily by Friday. Strong high pressure will quickly build east in the wake of a front well north of the state late Sunday through early next week, which will translate to strong to possibly gale-force trade winds (strongest over the channels and the typically windier zones). Models depict a storm to hurricane-force low developing near the date line south of the Aleutian Islands Thursday and Thursday night. Surf associated with this source should fill in locally through the overnight hours Saturday night before peaking through the day Sunday near or at High Surf Warning level (25 ft) for north facing shores. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 AM HST Thursday for Niihau-Kauai Windward-Kauai Leeward-Oahu North Shore-Oahu Koolau-Molokai-Maui Windward West-Maui Central Valley-Windward Haleakala-South Big Island-Big Island North and East. Small Craft Advisory until 6 PM HST Thursday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Channel-Oahu Windward Waters- Kaiwi Channel-Maui County Windward Waters-Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters. Small Craft Advisory until 6 AM HST Thursday for Kauai Leeward Waters-Oahu Leeward Waters. && $$ Public...Wroe Aviation...Eaton Marine...Powell