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Hurricane John Discussion Number 5

Wiki-Hurricanes Forecast Center

3:00 PM MDT Mon Aug 6 2018

John continues its rapid upward climb today. Infrared satellite imagery shows intense convection cooler than -70C over the center, while visible imagery depicts a cloud-filled eye. There haven't been any recent microwave passes of John, but given the aforementioned eye, the inner core is clearly better defined than this morning. Satellite intensity estimates were T3.5/55kt at 18z; however, UW-CIMSS ADT was at T3.9/63kt, with raw values near 75kt. Given the increased organization and reliance on CIMSS, the initial intensity has been raised to 70kt, making John a Category 1 hurricane.

The environment remains optimal for significant strengthening, with wind shear under 10kt, ocean temperatures above 30C, and mid-level relative humidity values near 75 percent. The SHIPS and LGEM continue to point to an intense hurricane over the next 48 hours, topping out at 121kt and 101kt, respectively. The new DTOPS rapid intensification model indicates an absurd 96% chance of 25kt/24hr development, with a 61% chance that John attains Category 4 strength over the next 36 hours. The GFS forecasts John to near Category 5 strength in 2 days, bottoming out at 924mb. It is interesting to note that the HMON and HWRF are not as aggressive as the other models, indicating minimum pressures of 967mb and 984mb, respectively. Given current trends and the environment at hand, however, these are being mainly disregarded for now. The updated forecast continues to make John a Category 4 hurricane within 36 hours, with rapid weakening thereafter as the storm enters ocean temperatures below 25C. Degeneration to a post-tropical cyclone is now expected by day 5.

John is moving steadily west-northwest toward a break in the mid-level ridge to its north. The storm should resume its earlier northwest motion over the coming hours and continue on that track until days 4 and 5, when it reaches the western periphery of the ridge and also becomes more dominated by low-level flow. Such a track should keep John west of Baja California.

FORECAST POSITIONS AND MAX WINDS

INIT 06/2100Z 70 KT 80 MPH

12H 07/0600Z 85 KT 100 MPH

24H 07/1800Z 100 KT 115 MPH

36H 08/0700Z 115 KT 130 MPH

48H 08/1800Z 120 KT 140 MPH

72H 09/1800Z 95 KT 110 MPH

96H 10/1800Z 65 KT 75 MPH

120H 11/1800Z 35 KT 40 MPH...POST-TROP/REMNT LOW