Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.
By: KoritheMan , 4:04 AM GMT on November 27, 2012
Tropical Cyclone Report
Chris was a high latitude hurricane that remained well out at sea over the north Atlantic shipping lanes.
a. Storm history
Chris developed from a weak cold front. Synoptic data indicate this front entered the western Atlantic on 13 June. An area of showers developed along the front as it progressed steadily eastward. An area of low pressure formed along the front early on 17 June while the system was centered about 250 miles southwest of Bermuda. As the low accelerated northeastward in lower- to middle tropospheric southwesterly flow, the overall satellite presentation and wind structure began to become better defined, with an ASCAT pass just after 0000 UTC 18 June indicating a broad surface circulation and increasing winds. Moving across the relatively warm waters of the Gulf Stream and through an environment of weak upper tropospheric shear, the system gradually developed symmetrical and relatively deep convection across roughly 75% of the center. This evolution led to the formation of a tropical storm around or just after 1800 UTC 19 June, when the system was located approximately 400 miles south-southwest of Cape Race, Newfoundland.
After genesis, Chris moved to the east-northeast under the influence of an upper low and its associated baroclinic zone located over Atlantic Canada. The cyclone turned northward early on 21 June, moving in a broad cyclonic fashion around the upper low. Just before 0000 UTC 21 June, an eye-feature began to develop in satellite and microwave data (not shown). As Chris turned northward, it became a hurricane near 1200 UTC while centered about 625 miles east-southeast of Cape Race, or about 1000 miles south of the southern tip of Greenland. Chris's strengthening over relatively cold underlying sea surface temperatures can probably be attributed to several meteorological phenomena: first, the chilly ocean temperatures, which are normally considered unfavorable for tropical cyclone formation and intensification, were likely mitigated by the very cold upper tropospheric temperatures in the surrounding environment as denoted on AMSU imagery at the time Chris became a hurricane (shown below). Second, Chris was located in close proximity to a large extratropical low pressure system to its south; northeasterly flow on the back side of this low probably acted to produce upper-level diffluence over the hurricane, a process that has been shown to aid in the development of convection. Lastly, the mean vertical shear pattern over eastward-moving Chris was nearly a uniform westerly when it began developing the eye. Finally, when Chris turned northward on 21 June, the upper tropospheric flow over the storm became more southerly.
This is another atmospheric process that has been shown to be conducive to the intensification of a tropical cyclone.When the two entities conflate and move in the same direction, the magnitude of the shear is generally reduced. Shortly after becoming a hurricane, Chris began to weaken. The eye became indistinct just after 1800 UTC, at which time Chris weakened to a tropical storm. Devoid of deep convection, the cyclone lost all tropical characteristics near 1200 UTC 22 June while centered about 350 miles east-southeast of Cape Race. Chris became absorbed into the extratropical low a few hours later.
b. Meteorological Statistics
Observations in Hurricane Chris include the satellite-based Dvorak intensity technique, AMSU microwave data, the Advanced Scatterometer (ASCAT), which was highly useful for tracking this marine cyclone, both in terms of track and intensity.
Chris's peak intensity of 65 kt is based on the incorporation of the Dvorak satellite interpretation method, where satellite estimates were firmly in the 4.0 range, considered the minimum threshold for hurricane intensity using the Dvorak method. Various microwave data were also used to assess the inner core structure of Chris. Fig 1 shows an AMSU microwave pass taken at 1825 UTC 21 June, after Chris had weakened back to a tropical storm. Fig 2 shows an SSMIS image shortly before 1200 UTC 21 June showing well the broad eye associated with the tropical cyclone. Fig 3 is a geostationary satellite picture of Chris at peak strength.
There have been no ship reports of tropical storm or hurricane force winds received in relation to Chris.
c. Casualty and Damage Statistics
Since it remained out at sea throughout its lifetime, there were no reports of damage or fatalities associated with this cyclone.
The track errors associated with Chris were exceptionally small, although the hurricane was too short-lived to gain a meaningful quantitative forecast evaluation.
Initial forecasts called for much less strengthening than actually occurred, likely due to the baroclinic environment in which the storm was embedded. When it became apparent that Chris would strengthen significantly, later intensity forecasts were more bullish.
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.
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