The extratropical transition of Tropical Storm Ophelia (2005): Summary of forecasts and meteorological observations

During the 2005 Atlantic Hurricane season, Hurricane Ophelia skirted along the outer banks of North Carolina on 15 September and accelerated toward Nova Scotia while undergoing extratropical transition (ET). A shortwave trough moving eastward from the Great Lakes introduced significant vertical wind shear over the storm (up to 20 m s-1) and very dry midlatitude air which tore apart the upper portion of the circulation (above 600 hPa) on 17 September. Ophelia became extratropical when it arrived at the coast of Nova Scotia as a 45-kt (23-m s-1) storm bringing heavy rains and gusty southeasterly winds.

The NOAA Hurricane Research Division and the Meteorological Service of Canada conducted two observational research flights into Ophelia during its ET phase as part of the 2005 Intensity Forecasting Experiment (IFEX). The first flight took place on 16 September as Ophelia was beginning transition. The second flight was conducted on 17 September when the storm was becoming sheared apart by strong southwesterly winds aloft. Cross-sectional analyses of dropwindsonde data will be presented and compared with large scale synoptic weather analyses and surface meteorological data.

Many forecast challenges were present during the ET of this event, primarily because of the oblique angle at which Ophelia was to approach the Nova Scotia coastline, and some uncertainty as to whether modest baroclinic intensification would occur as indicated by some numerical models. The Canadian GEM model appropriately forecast the shearing-apart and dry-air intrusion into the storm on 17 September, yet overpredicted the storm's intensity. Several weather warnings were posted by the Canadian Hurricane Centre and local weather office which did not materialize. There was a significant overreaction from the media which compounded the problem. This case not only highlights the existing numerical and operational forecast challenges associated with ET, but also the challenges of conveying warnings and forecast confidence to the public.