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Tropical Storm Kristy Discussion Number 3

Wiki-Hurricanes Forecast Center

8:00 AM PDT Tue Aug 7 2018

Kristy appears to be slowly organizing this morning as it shields itself from some dry air attempting to settle inwards from an upper-level low diving to the tropical storm's north. Kristy has developed a fairly traditional curved band appearance, with all the typical ragged edges of a newly developed tropical system. There have been no new infrared passes to probe at the inner structure of the tropical storm, but curved band structures on infrared are often well reflected in microwave data. Cirrus-demarked outflow is evident in all quadrants, but is most favorable equatorward while it apepars to be suppressed to the storm's north. UW-CIMSS estimated T2.8/41kt with SAB and TAFB both estimating T3.0/45kt. A blend of these yields an initial intensity of 45 kt.

Environmental conditions are generally favorable for intensification. Currently, the atmosphere is adequately moist, and sea surface temperatures are conducive for convective development. The main inhibiting factor in the short term is a shortwave trough to the tropical storm's northwest that is resulting in some northerly to northeasterly wind shear of around 15 kt over the system. SHIPS shows decreasing wind shear and favorable upper-level winds in a day's time, though some guidance suggests a small upper-level low passing to Kristy's northeast may impart some shear on the system in about two days. A combination of unfavorable features, mostly caused by cooler ocean waters, should weaken the system once it reaches the 20th parallel in three to four days. Both SHIPS and LGEM show a high end tropical storm, with HMON in agreement. The GFS favors a low-end hurricane, and HWRF serves as a high-end outlier with a Category 2, though this seems a bit unrealistic given the low sea surface temperatures the model indicates. On the other end of the spectrum, both ECMWF-IFS and UKMO-G show not much more than a weak to moderate tropical storm. Given generally favorable conditions, the current forecast shows a high-end tropical storm, though a minimal hurricane is certainly posible.

Kristy has somewhat unexpectedly slid southwest of forecast, perhaps due to the orientation of subtropical ridging over the southwestern United States. The main question mark arises over how much influence the nearby Hurricane John will exert in Krtisty's motion, especially in the pivotal two to three day range. Currently, it is anticipated that both Kristy and John will be strong enough to pull eachother towards a common center of circulation, which should materialize as a northward turn for Kristy. However, Kristy's forecast track is one of the more extreme examples of the variable impact of intensity on Kristy. As the strongest reliable model, the HWRF makes Kristy the dominant cyclone in a Fujiwhara interaction with John, keeping it on an east-northeasterly track all the way to the 30th parallel north. In the meanwhile, the ECMWF-IFS keeps Kristy fairly weak, and doesn't show much interaction with John at all, keeping Kristy on a west-northwesterly path in line with the flow of the subtropical ridge. For now, an interaction with the large circulatio of Hurricane John is favored, and a curve north is anticipated before a rebolstering of the ridge enables a westerly turn in around four to five days. John and Kristy may be too far apart to effectively merge.

FORECAST POSITIONS AND MAX WINDS

INIT 07/1500Z 45 KT 50 MPH

12H 08/0000Z 50 KT 60 MPH

24H 08/1200Z 55 KT 65 MPH

36H 09/0000Z 60 KT 70 MPH

48H 09/1200Z 60 KT 70 MPH

72H 10/1200Z 55 KT 65 MPH

96H 11/1200Z 45 KT 50 MPH

120H 12/1200Z 35 KT 40 MPH