ZCZC HFOTCDCP1 ALL TTAA00 PHFO DDHHMM Hurricane Walaka Discussion Number 13 NWS Central Pacific Hurricane Center Honolulu HI CP012018 1100 AM HST Tue Oct 02 2018 Morning visible and infrared satellite imagery trends showing Walaka has degraded somewhat over the past several hours. The eye has become less distinct with a clouds apparently partially covering the eye. Cloud tops have warmed in the eyewall and surrounding convective ring, and Dvorak intensity estimates started to follow this weakening trend which began overnight. Current intensities range from 6.0 at SAB to 6.5 at PHFO and JTWC. Have conservatively lowered the initial intensity to 130 kt for this forecast cycle as Satcon estimates as of 1528 UTC were at 132 knots, with a very slow weakening in the short term as Walaka appears to be completing an eyewall replacement cycle based on earlier composite microwave data overnight. A solid ASCAT pass from 0816 UTC was useful to make minor adjustments to the wind radii, and an altimeter pass aided in adjusting the 12 foot seas radii. The initial motion was set at 355/09 knots, as Walaka continues to be drawn northward by the deep low pressure system to the north. This motion is expected to continue over the next day or two with some acceleration as the influence of this low pressure over the Walaka steering currents increases. By Thursday and Friday, Walaka slows as it interacts with the mid latitude trough which remains cutoff from the mid latitude westerlies aloft. By early Saturday, another sharp upper trough picks the tropical cyclone up and shifts it off to the northeast through the weekend, resulting in accelerating northeastward motion. Overall, the track guidance envelope remains fairly tightly clustered through Friday, with some variations on how quickly Walaka gets picked up by the westerlies over the weekend. The official forecast stays very close to the previous advisory and is only slightly nudged towards HCCA and ECMWF beyond Friday. Although experiencing a weakening trend since last night, the environment surrounding Walaka remains somewhat conducive for intensification during the next 12 to 18 hours. The tropical cyclone will remain within a deep moist airmass with low vertical wind shear, high ocean heat content and sea surface temperatures near 29 or 30 degrees C. The forecast shows continued weakening in the short term, due to current trends, then steady intensity tonight through early Wednesday, as this period has the potential for another round of intensity fluctuations within aforementioned conducive conditions. Between 24 and 48 hours, vertical wind shear increases dramatically due to interaction with the upper level jet around the deep low to the north, resulting in steady and rapid weakening of Walaka especially Thursday and Friday. Weakening trend relaxes Saturday and Sunday as Walaka accelerates to the northeast and transitions to an extratropical cyclone. The official forecast follows the SHIPS and dynamical intensity consensus through the 5 day forecast, except holds the intensity up through the first 24 hours owing to potential fluctuations. The forecast track will take Walaka near Johnston Island later today, with hurricane conditions expected this afternoon and this evening. Therefore a Hurricane Warning remains in effect for this location. The forecast track also takes the hurricane across the Papahanaumokuakea Marine National Monument between French Frigate Shoals and Maro Reef late Wednesday, therefore, a Hurricane Warning has been issued for this area. A Tropical Storm Warning has been issued east of French Frigate Shoals to Nihoa as tropical storm conditions are expected to reach that area late Wednesday. FORECAST POSITIONS AND MAX WINDS INIT 02/2100Z 15.6N 170.1W 130 KT 150 MPH 12H 03/0600Z 17.4N 169.9W 125 KT 145 MPH 24H 03/1800Z 20.5N 169.1W 125 KT 145 MPH 36H 04/0600Z 23.9N 167.8W 110 KT 125 MPH 48H 04/1800Z 27.0N 167.3W 85 KT 100 MPH 72H 05/1800Z 31.0N 167.2W 65 KT 75 MPH 96H 06/1800Z 35.3N 162.7W 55 KT 65 MPH 120H 07/1800Z 44.6N 154.2W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Brenchley NNNN
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Page last modified: Monday, 13-May-2019 15:53:17 UTC