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Tropical Storm Kristy Discussion Number 4

Wiki-Hurricanes Forecast Center

2:00 PM PDT Tue Aug 7 2018

Yikes. Kristy appears to have taken a large gulp of dry air this afternoon, eating away at the storm's central convection and reducing the center of circulation into a dense low-level cumulus field. The storm's deepest convection is limited to a frazzled curved band that wraps around the outside of the center of circulation, and even then this convective activity is not particularly deep. The culprit appears to be a burst of dry air aided by an upper-level low, accelerating the subsident air towards Kristy and injecting it into the storm's preexisting dry slot. AMSU microwave imagery from 1824Z showed a convectively-exposed center of circulation, though a decent structure and convective traces are still present for future shower activity to develop if conditions permit. SAB at 18z provided a T3.5/45kt satellite estimate on the spiral band, while ADT final values are by protocol lagging behind falling raw data values but are currently at T2.7/39kt. An ASCAT pass from 1825Z still showed a swath of gale-force winds confined to the northeastern quadrant, topping to 35 kt. Given the general 5 kt rule of thumb for undersampling, the current intensity for Kristy has been lowered to 40 kt.

Kristy is tracking slowly westward under the influence of subtropical ridge centered over the western United States, though with Hurricane John providing some steering interference, this ridge does not exert much steering flow over the tropical storm, and thus Kristy is tracking fairly slowly. Models reflect a spectrum of scenarios between Kristy banking hard right turn towards John to John exerting minimal influence, allowing Kristy to return to the overall subtropical steering flow and track west-northwest. The differences appear to stem from a difference in modeled intensities as a stronger cyclone would more likely pull towards John. Conditions are somewhat favorable for intensification, though upper-level winds may be less than favorable given the number of small localized upper-air disturbances in the region, resulting in some shear that is allowing subtropical dry air to seep into Kristy's circulation. Despite the early afternoon hiccup, intensification continues to be depicted before cooling waters underuct the system's intensity, allowing the system to degenerate into a remnant low in 120 hours.

FORECAST POSITIONS AND MAX WINDS

INIT 07/2100Z 40 KT 45 MPH

12H 08/0600Z 45 KT 50 MPH

24H 08/1800Z 50 KT 60 MPH

36H 09/0600Z 60 KT 70 MPH

48H 09/1800Z 60 KT 70 MPH

72H 10/1800Z 50 KT 60 MPH

96H 11/1800Z 35 KT 40 MPH

120H 12/1800Z 30 KT 35 MPH...POST-TROP/REMNT LOW