{"id": "1212758789099225095", "title": "Tropical Cyclone Discussion", "adv_date": "2026-09-23T15:00:00Z", "msg": "269\nWTPA42 PHFO 231449\nTCDCP2\n \nTropical Depression Fifteen-E Discussion Number  12\nNWS Central Pacific Hurricane Center Honolulu HI   EP152026\nIssued by NWS National Hurricane Center Miami FL\n500 AM HST Wed Sep 23 2026\n\nSatellite imagery shows that the depression is becoming better \norganized.  Banding features are becoming more defined on the \nwestern and northern sides of the system, with expanding outflow \nnoted.  However, the low-level circulation appears to be on the \nsoutheastern edge of the deep convection and isn't well aligned \nwith the deep convective mass.  Satellite intensity estimates have \na large spread this morning, from about 25-40 kt.  Without \ndefinitive evidence it has become a tropical storm, the initial wind \nspeed will stay 30 kt, which is also consistent with winds from a \nrecent OSCAT scatterometer pass.\n\nThe depression has slowed since the last advisory and seems to be \nmoving west-northwestward at about 5 kt.  A ridge to the northeast \nof Hawaii is forecast to weaken and slide eastward as a mid- \nlatitude trough drops over the northwestern Hawaiian islands.  \nThis evolution is likely to the cause the cyclone to slow down \nlater today or tonight and then turn northward or north- \nnortheastward by tomorrow with some increase in forward speed. The \ntrough is forecast to move westward this weekend as the ridge \nrebuilds north of Hawaii, which should force a sharp westward turn \nwhile the cyclone is close to the Big Island.  At this time frame, \nit is impossible to know exactly when that turn will happen and, \nunsurprisingly, there is a large north-south spread in the guidance. \nOur best guidance is on the northern side of the track envelope, \nand new NHC forecast remains essentially the same as the last \nadvisory.  Interests in the Hawaiian Islands, especially on the Big \nIsland, should closely monitor the system, with life-threatening \ncatastrophic flooding possible over the steep terrain on this track.\n\nThe depression should intensify slowly at first, given the current \nstructure of the low-level center not co-located with the mid-level \ncirculation as seen on satellite.  However, after the system \ndevelops an inner core, the environment seems conducive for \nsignificant strengthening, with low shear, high mid-level moisture \nand SSTs from 28-29C.  The rapid intensification probabilities are \nincreasing, and the best model guidance is showing this as a major \nhurricane in a few days.  Given the environment and the \nbest-performing aids (Google DeepMind and HCCA) again showing \nmajor-hurricane strength, the NHC forecast is raised from the \nprevious one and shows the cyclone as a major hurricane when it \napproaches the Big Island of Hawaii by the weekend.\n \nKey Messages:\n \n1. Tropical Depression Fifteen-E is expected to strengthen into a \ntropical storm later today and a hurricane on Thursday as it turns \nnorthward, potentially making its closest approach to the Big Island \nof Hawaii on Saturday. There is an increasing risk of wind and wave \nimpacts in the Hawaiian Islands, and a Hurricane Watch may be \nrequired for the Big Island later today.\n\n2. The time to prepare for significant heavy rain and flooding \nimpacts on the Big Island is now, as heavy rain becomes more likely \nby Thursday and Friday.  Periods of heavy rain are likely to \ncontinue across the Big Island and Maui through the weekend. \nLife-threatening, catastrophic flooding and mudslides are possible, \nespecially in areas of steep terrain across the Big Island and Maui. \nAcross the remainder of Hawaii, lesser rainfall totals are expected, \nwith isolated flooding possible. \n\n3. Interests in Hawaii should closely monitor the latest forecast \nupdates and ensure that they have their preparedness plan in place. \n \nFORECAST POSITIONS AND MAX WINDS\n \nINIT  23/1500Z 14.5N 154.4W   30 KT  35 MPH\n 12H  24/0000Z 14.7N 155.2W   40 KT  45 MPH\n 24H  24/1200Z 15.0N 155.5W   50 KT  60 MPH\n 36H  25/0000Z 15.7N 155.2W   65 KT  75 MPH\n 48H  25/1200Z 16.7N 154.8W   80 KT  90 MPH\n 60H  26/0000Z 17.6N 154.5W   90 KT 105 MPH\n 72H  26/1200Z 18.2N 154.7W  100 KT 115 MPH\n 96H  27/1200Z 18.1N 157.0W  100 KT 115 MPH\n120H  28/1200Z 18.7N 160.2W   95 KT 110 MPH\n \n"}