Session 6B.1 Dynamical structures and precipitation distributions of transitioning tropical cyclones in Eastern Canada, 1979–2004

Tuesday, 2 August 2005: 8:00 AM
Empire Ballroom (Omni Shoreham Hotel Washington D.C.)
Shawn M. Milrad, McGill University, Montreal, QC, Canada; and E. Atallah and J. R. Gyakum

Presentation PDF (2.0 MB)

From 1979-2004, 33 storms originally tropical in nature (as classified by the National Hurricane Center) have affected Eastern Canada to various degrees during or after extratropical transition. This study examines the dynamical structure of these 33 cases from a QG perspective using the Trenberth approximation to the QG omega equation (advection of mid-tropospheric vorticity by the thermal wind), primarily utilizing the NCEP North American Regional Reanalysis (NARR) dataset. Via the Trenberth approximation method described above, we were able to partition the storms into two groups, "intensifying" and "decaying", based upon the quasigeostrophic forcing for ascent. In addition, we analyze the precipitation distribution of the cases in the study using the 3-hour accumulated precipitation field in the NARR. Composites of both partitioned groups have been completed for several mass fields and will be presented. Furthermore, both the 'good' and the 'bad' of the NARR will be shown, including Canadian precipitation assimilation problems, precipitation over the oceans, comparisons with the NCEP global reanalysis, etc. Hurricane Juan (2003) will be highlighted as a particular failure for the NARR.
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