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Tropical Storm John Discussion Number 18

Wiki-Hurricanes Forecast Center

8:00 PM PDT Thu Aug 9 2018

John has managed to keep it together as it slowly winds down over the cooler waters of the Pacific above the 25th parallel north. Satellite imagery from this afternoon and evening show a compact area of organized convective activity still keeping steady with the center of circulation, though there are some signs that this convection is getting set to begin fading away as the shower activity does not appear to be a cohesive as earlier and is beginning to become diffuse, with storms lifting upwards into decaying cirrus. Microwave imagery also indicates that the deep convection is beginning to tilt away from the surface circulation, and could leave the vortex barren by tomorrow. Raw T-values from UW-CIMSS ADT are near T2.8/41kt, while current intensity estimates from SAB and TAFB at T4.5/45kt and T3.5/55kt, respectively. Most visible indicators are indicative of continued weakening, so even despite the false cirrus eye seen on the latest satellite images I am decreasing the intensity of John further to 50 kt.

John's motion has gradually become more west-northwest than northwest due to its shrinking vertical profile and the presence of a 594 dm ridge centered over the US Great Basin. An approaching shortwave trough is expected to weaken the ridge, causing it to regress eastward and allowing for a slow drift of John towards the northeast as a weak degenerate low. In the meantime, John is already traversing sea surface temperatures below 24°C which should allow for the continued slow decline in convective activity, in lieu of other unfavorables. The forecast for John remains the same intensity-wise.

MAXIMUM WINDS FORECAST

INIT 10/0300Z 50 KT 60 MPH

12H 10/1200Z 45 KT 50 MPH

24H 11/0000Z 40 KT 45 MPH

36H 11/1200Z 35 KT 40 MPH

48H 12/0000Z 30 KT 35 MPH...POST-TROP/REMNT LOW

72H 13/0000Z 25 KT 30 MPH...POST-TROP/REMNT LOW

96H 14/0000Z 20 KT 25 MPH...POST-TROP/REMNT LOW

120H 15/0000Z...DISSIPATED