Tropical Storm Ileana Discussion Number 23
Wiki-Hurricanes Forecast Center
8:00 AM PDT Mon Aug 6 2018
Another day, another new cycle of convection from Ileana. Beginning at around 06z, a new burst of convection near Ileana's center of circulation exploded quite impressively and now appears to be serving as the unusual tropical cyclone's core structure for today. This latest burst of convection appears to be better aligned with the low-level center of circulation and appears to be more well-defined then previous diurnal convective bursts. In fact, microwave data from 1247Z show an exceptionally stout mid-level circulation rounding off an embedded center with bands spiraling inwards. Long-range radar from Acapulco also shows this circulation and what appears to be the beginnings of some sort of eyewall that is strongest to the northeast wrapping inwards. It is unclear what is occuring specifically at the surface, but a powerful mid-level circulation can impart strong winds of similar magnitude at the surface, particularly when convection is as strong as it has been. SAB continued their T3.0/45kt estimate this morning, though in acknowledging last night's ASCAT pass suggestive of winds above 45 kt, the intensity has been increased to 55 kt.
Ileana's west-northwest to northwesterly motion is being dictated by an inverted mid-level trough now beginning to move into the Gulf of California. Later today, however, Ileana should come close enough to the strengthening Tropical Storm John--possibly a hurricane by that time--such that John becomes the dominant steering feature. John's circulation and pressure field are much more distinct compared to Ileana's, so over time Ileana should curve west in a process of absorption. Models have come to slightly more agreement in the absorption scenario, though a good portion still keep Ileana cruising towards the northwest in a straightforward manner. For this advisory, the current forecast expects John to eventually absorb Ileana.
Ileana has managed to strengthen in the face of a very chaotic atmosphere thanks to the strength of its convection, and perhaps there is opportunity for the storm to strengthen even further if it can work against the grind of 15-25 kt northerly shear as lapse rates remain high with more than enough moisture to fuel thunderstorms. Ileana will continue to pulse diurnally, perhaps four times a day in line with the diurnal atmospheric cycles of the Pacific Ocean and North America. As Ileana wraps around John, the centripetal acceleration could maintain strong winds though the internal core structure would be elongated and stretched apart. The current forecast shows some intensification before weakening commences tomorrow, with absorption occuring in 48 hours. However, this demise could occur sooner.
FORECAST POSITIONS AND MAX WINDS
INIT 06/1500Z 55 KT 65 MPH
12H 07/0000Z 60 KT 70 MPH
24H 07/1200Z 55 KT 65 MPH
36H 08/0000Z 50 KT 60 MPH