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Chris Discussion -- 8/1/06
      #68785 - Tue Aug 01 2006 02:31 PM

Earlier this morning, the third named tropical cyclone of the 2006 season, Chris, was classified by the NHC. Currently, the system remains a weak tropical storm with an intensity of 40mph/1009mb as it is being influenced by some northerly shear. An upper level low (ULL) is located about 900 miles to the northwest of the tropical storm and is moving slowly westward underneath a building ridge of high pressure in the midlatitudes. A weaker ULL is located about 600 miles to the east-northeast of the tropical storm and is only having a minimal impact upon it at this time. The current 5-day NHC forecast shows some modest strengthening as Chris heads toward the west-northwest in the general direction of the Bahamas and South Florida.

Intensity and track are the two main questions with Chris. The cloud and convective pattern is slowly trying to become better organized, but is doing so in fits and spurts. The ULL to the east of the storm is serving to slightly enhance its outflow, while the ULL to the northwest of the storm largely is not affecting Chris at this time. The current synoptic pattern suggests that the eastern ULL should get caught up in the approaching upper trough off of the coast of Nova Scotia and not impact Chris much longer, while the western ULL should begin to accelerate toward the west underneath a building ridge of high pressure across the eastern US and western Atlantic. Question is, how close does Chris get to this latter ULL before it begins to accelerate to the west? Too close and Chris could be sheared apart, while only a slight bit closer from here could lead to a favorable regime with an outflow channel and diffluent winds aloft.

Models are unanimous in forecasting the building of this ridge across the east -- it's going to be a hot rest of the week along the eastern seaboard, it seems -- and the development of a significant cut-off low off of the coast of California concordant with the development of a Rex (high over low) block in that region. This favors ridging across much of the southern tier of states, albeit becoming slightly more elongated through time. Furthermore, in the Atlantic, the ridging is projected to hold across the basin and be significant enough to steer that upper low toward the west through time. The GFS even predicts the development of an extension to the ridge between the retrograding upper low and Chris.

I tend to favor this projected evolution. While the convection associated with Chris is currently lopsided toward the south, as it becomes better organized and the northerly shear abates somewhat, warming impacts from its upper-level outflow should begin to help amplify the ridge in its immediate vicinity somewhat and keep the negative impacts of the retrograding ULL at bay. The GFS shows the development of another cut-off ULL to the east of Chris later in the forecast period, but I am not sold on this evolution; I believe the amplification of the pattern across the Atlantic will be sufficient to favor transient patterns rather than blocky, trough fracture favoring patterns. I do not feel that the relatively dry environment in the region will be a significant factor against Chris' development, particularly as the shear decreases somewhat.

What does all of this mean? Chris will likely intensify only slightly for the next 24-48 hours while the upper level pattern slowly becomes more favorable. After that, I except some more significant intensification, likely to cat 1-2 hurricane strength before the five day period is out. It is somewhat of an all-or-nothing scenario, where it either remains weak and is torn apart or it gets into an environment favorable for some decent strengthening. As of now, I tend to favor the latter. The storm should gradually move to the west-northwest over the next 24-48 hours before bending back slightly more toward the west and perhaps accelerating just a touch -- it's moving at 10mph, nothing more than 13mph or so is expected -- as it begins to feel greater impacts from the building ridge. The NHC track looks pretty good from here. This would place the northern Bahamas and southern Florida under the gun in the 4-5 day time frame.

After that, the forecast depends upon the evolution of the developing block off of the coast of California; if this opens up, there will likely be a significant trough to capture and start to recurve the storm, whereas if not the storm may be able to proceed more or less toward the west-northwest in the Gulf. WAY too early to speculate any further, however. There will be plenty of time to look at that as we approach the weekend.

For now though, watch Chris over the next day or so and be wary of any sudden increase in organization or retrogression of the ULL to its west.

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