Monday, November 1, 2010

From hurricane to weak storm: Tomas



Tomas weakened rapidly as "shear" tore it apart. It became obvious this wasnt upper level shear but rather midlevel shear as the mid-level vortex decoupled from the low-level vortex. Animations of this period show a very strong band of convection to the southeast actually develop its own outflow signature. This area of convection persisted even as Tomas' CDO  decayed to reveal the low level swirl this morning. The upper level shear probably did change as Tomas excellent outflow was virtually absent in the southern quadrant. Deep convection refired late in the morning but was pretty ragged and the HH aircraft found Tomas significantly weakened and disorganized.

hard to know what may have actually happened, but I am stuck wondering what role the SE area of convection played in Tomas demise, more specifically how that area of convection established its own outflow and how that interacted with Tomas. Also, what was the decoupling mechanism and how vertically confined was it to shear the vortex apart and only briefly stall deep convection?

Anywho, this is not my area of expertise. I am interested in where Tomas goes and how it interacts with the cutoff cyclone in the Gulf by Saturday.

 The GFS takes the upper level low into the gulf where it rapidly weakens in 18 hours, though the effects of the low may be felt very far south as a cold surge. Though cold might be a relative term. The GFS is rampant with parameterized convective rainfall and that could be one mechanism for the destruction of PV aloft. The other mechanism for not leaving the cutoff over the gulf is another disturbance on the dynamic tropopause that crosses the ridge  and helps keep moving things along.

Either way how things play out with Tomas and the cutoff low is rather interesting from a predictability standpoint, for all the individual elements (TC, cutoff low, cold surge, and heavy rainfall for Florida, Cuba and Haiti). Expect some impacts from this entanglement. In the meantime I need to look closely at the GFS ensemble.