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Hurricane John Discussion Number 9

Wiki-Hurricanes Forecast Center

2:00 PM PDT Tue Aug 7 2018

John has not intensified this afternoon. While the eye has become more distinct on infrared and visible channels, a 1721Z AMSU microwave pass indicated that the eyewall was open to the northwest, and the extent of deep convection has decreased since this morning. Satellite intensity estimates range from T4.5/77kt from SAB to T5.0/90kt from TAFB to T5.6/105kt from UW-CIMSS ADT, with raw values from the latter system also around 90kt. A blend of these values supports an intensity of 90kt; however, the initial strength has been assessed at 95kt given the more distinct eye.

SHIPS analyzed wind shear at 14kt, which, alongside John's large size, may explain the persistent intrusions of dry air into the core. This shear is expected to lessen over the following days, presenting an opportunity for some intensification as the hurricane remains over waters warmer than 29C. By tomorrow night, however, John will be passing over the 26C isotherm into a cooler and drier environment, which should cause rapid weakening. The updated forecast shows the system regaining major hurricane strength later tonight, with degeneration in four days.

John is moving northwest around the western periphery of a mid-level ridge to its north. As the hurricane weakens and becomes influenced by low-level flow, it should turn toward the west. The center of the hurricane is expected to pass west of Baja California Sur, although fringe effects are possible still.

FORECAST POSITIONS AND MAX WINDS

INIT 07/2100Z 95 KT 110 MPH

12H 08/0600Z 100 KT 115 MPH

24H 08/1800Z 95 KT 110 MPH

36H 09/0600Z 80 KT 100 MPH

48H 09/1800Z 60 KT 70 MPH

72H 10/1800Z 40 KT 45 MPH

96H 11/1800Z 30 KT 35 MPH...POST-TROP/REMNT LOW

120H 12/1800Z 25 KT 30 MPH...POST-TROP/REMNT LOW