Hurricane John Discussion Number 7

Wiki-Hurricanes Forecast Center

2:00 AM PDT Tue Aug 7 2018

John is rapidly intensifying again. Shortly after 23z, the hurricane began firing extremely deep convection within its eyewall. This convection continued to grow and rapidly encapsulate the eye, a process that continues to the current time. Recent microwave passes reveal that John has transitioned from a curved band to a legitimate inner core, with a more symmetrical appearance that may help keep environmental dry air at bay. Satellite intensity estimates from SAB and TAFB were T5.0/90kt and T4.5/77kt, respectively. UW-CIMSS ADT posted a final value of T4.3/72.2kt, but raw estimates have climbed above 115kt. Manual Dvorak analysis as of the time of this advisory, meanwhile, yields T5.5/102kt. A blend of all these values supports raising the initial intensity to 90kt and making John a Category 2 hurricane.

The intensity forecast remains complex. The earlier discussion noted concerns about environmental dry air thanks to the large size of Hurricane John, and these fears remain, although they've taken a back seat in light of the dramatic shift in satellite appearance since that time. Wind shear is light and ocean temperatures remain exceptionally warm, yielding an 85% chance of 25kt/24hr RI and a 53% chance of 40kt/24hr RI from DTOPS. The SHIPS and LGEM make John a Category 4 and Category 3 hurricane, respectively, with the HWRF siding with LGEM. The GFS, on the other hand, shows John becoming an upper-end Category 4 hurricane. The HMON remains wholly uninterested in intensifying the storm. For now, the updated forecast has been adjusted upward again, although not as high as it may need to be given recent trends. After 36 hours, John should enter increasingly cool waters and weaken rapidly, degenerating to a remnant low around 4 days from now.

John is moving northwest toward a weakness in the mid-level ridge to its north, and this track should continue for the next three days unabated. By days 4 and 5, a more shallow tropical cyclone should curve toward the west. While the center of John is expected to remain west of Baja California, fringe effects are expected. A slight shift east would bring more significant impacts.


INIT 07/0300Z 90 KT 105 MPH

12H 07/1200Z 100 KT 115 MPH

24H 08/0000Z 105 KT 120 MPH

36H 08/1200Z 110 KT 125 MPH

48H 09/0000Z 100 KT 115 MPH

72H 10/0000Z 80 KT 90 MPH

96H 11/0000Z 40 KT 45 MPH...POST-TROP/REMNT LOW

120H 12/0000Z 30 KT 35 MPH...POST-TROP/REMNT LOW

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