Convective Contribution to the Genesis of Hurricane Ophelia (2005) Robert A. Houze, Jr. University of Washington Wen-Chau Lee and Michael M. Bell National Center for Atmospheric Research Seminar at National Hurricane Center, Miami, 25 August 2008

Mesoscale convective system lifecycle ~200 km ~100 km

Convection in an intensifying tropical depression--idealized Ritchie & Holland 97 Bister & Emanuel 97 Zipser & Gautier 78 Hendricks et al. 03 Montgomery et al. 06

Hurricane Ophelia (2005) Ophelia formed from a non-tropical weather system. A cold front moved off the eastern coast of the United States on 1 September. The front moved southeastward and became part of an elongated trough of low pressure that extended from Tropical Depression Lee east of Bermuda to near the Florida Peninsula. Two areas of low pressure formed in the trough on 4 September. The eastern low, south of Bermuda, eventually became Hurricane Nate. The western low, near the Bahamas, became Ophelia.

Ophelia formed from a non-tropical weather system Ophelia formed from a non-tropical weather system. A cold front moved off the eastern coast of the United States on 1 September. The front moved southeastward and became part of an elongated trough of low pressure that extended from Tropical Depression Lee east of Bermuda to near the Florida Peninsula. Two areas of low pressure formed in the trough on 4 September. The eastern low, south of Bermuda, eventually became Hurricane Nate. The western low, near the Bahamas, became Ophelia. 500 mb

NOAA Hurricane Field Program Flight Plan for “Convective Burst”

dBZ, vorticity, pv

For whole volume. Outliers in cell For whole volume. Outliers in cell. Bulk of mass transport is by moderate updrafts. These are probably the remnants of previously strong cells. --> stratiform

Stratiform region Strat refl. Probably remnants.

Stratiform region

Stratiform region No downdraft

Stratiform region sounding (“onion sounding”)

Stratiform region 30 20 10

Convection in an intensifying tropical depression--idealized Ritchie & Holland 97 Bister & Emanuel 97 Zipser & Gautier 78 Hendricks et al. 03 Montgomery et al. 06

Conclusions Convective cells extremely deep & intense Downdraft outflow convergence absent--buoyancy probably due to wind-induced mixing PV generated in convective cells at low-mid levels Stratiform region accumulates vorticity generated in cells Vorticity in both convective and stratiform regions is axisymmetrized into the parent vortex Stratiform region downdrafts not significant Bullet 1--Zipser Bullet 2--Crook & Moncrieff Bullet 3--Zipser/Gautier, Montgomery Bullet 4--Montgomery Bullet 5--Bister & Emanuel

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