ZCZC HFOTCDCP2 ALL TTAA00 PHFO DDHHMM Hurricane Lane Discussion Number 31 NWS Central Pacific Hurricane Center Honolulu HI EP142018 1100 PM HST Tue Aug 21 2018 Lane remains an impressive hurricane this evening, with a well- developed warm eye completely surrounded by persistent cold cloud tops. Outflow remains best to the north through east and is slightly restricted elsewhere. Hurricane Hunter aircraft from the 53rd Weather Reconnaissance Squadron flew through Lane once again this evening, shortly after the last forecast package, and found winds within the northeast eyewall of 146 kt. Based on this observation, a special forecast package was issued strengthening Lane to a catagory 5 hurricane. Subjective Dvorak current intensity estimates range from 6.5/127 kt (JTWC and SAB) to 7.0/140 kt (PHFO). ADT from UW-CIMSS was 132 kt. Based on a blend of aircraft-observed central pressures and wind speeds, we will set Lane's initial intensity to 140 kt for this package. Initial motion for this advisory is 285/8 kt. Lane has been moving generally westward along the southern flank of a mid-level ridge during the past several days. However, this cyclone will soon begin to round the western periphery of this ridge and move into an area of relatively light steering flow. This will allow Lane to gain latitude as its forward speed diminishes. Lane is forecast to continue moving west-northwest tonight, then turn to the northwest on Wednesday, and to the north-northwest on Thursday, as it moves between the mid-level ridge to the east and a developing upper-level trough to the northwest of Hawaii. The track and intensity forecasts become increasingly uncertain after this point as most track guidance brings Lane very close to the islands, with potential interaction between Lane and the mountainous terrain of the islands. UW-CIMMS derives 13 kt of vertical shear now and this is forecast to increase to 20 to 30 kt at 48 hours, according to ECMWF SHIPS. The combination of land interaction and increasing vertical shear leads to a weakened Lane being steered to the west by the low-level trade wind flow during the later forecast periods. The new track forecast closely follows the previous one and lies between GFS and ECMWF along FSSE. Water temperatures along the forecast track will be 27 to 28 degrees C, warm enough to support a major hurricane. Any significant weakening as Lane draws closer to the Hawaiian Islands will likely be due to increasing wind shear. Through the next 36 to 48 hours, shear is expected to remain in the 10 to 20 kt range, and we expect only slow weakening initially. At 48 hours and beyond, the forecast incorporates an expected sharp increase in shear as Lane moves closer to the large upper trough to the northwest of the main Hawaiian Islands. The new intensity forecast is very similar to the previous forecast, situated firmly between the EMXI and IVCN ensemble guidance. KEY MESSAGES: 1. Lane is forecast to move dangerously close to the main Hawaiian Islands as a hurricane Thursday through Saturday, potentially bringing damaging winds and life-threatening flash flooding from heavy rainfall. As Lane is expected to be slow-moving as it nears the islands, it will produce large and damaging surf. 2. As Lane approaches the islands from the southeast, initial impacts will be felt on the Big Island, where a Hurricane Warning is in effect. Preparations should be rushed to completion as tropical-storm force winds are forecast to arrive by late Wednesday or early Thursday. A Hurricane Watch remains in effect for Maui County and the island of Oahu, with tropical-storm force winds possibly beginning Thursday or Thursday night. 3. Do not focus on the exact forecast track for Lane, as life- threatening weather conditions extend well away from the center of the hurricane, and impacts could be felt on any of the islands. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 14.7N 154.5W 140 KT 160 MPH 12H 22/1800Z 15.4N 155.6W 135 KT 155 MPH 24H 23/0600Z 16.6N 156.3W 125 KT 145 MPH 36H 23/1800Z 17.8N 157.0W 110 KT 125 MPH 48H 24/0600Z 19.1N 157.6W 95 KT 110 MPH 72H 25/0600Z 21.0N 159.4W 70 KT 80 MPH 96H 26/0600Z 21.2N 162.2W 50 KT 60 MPH 120H 27/0600Z 20.8N 165.3W 40 KT 45 MPH $$ Forecaster Powell NNNN
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