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Thursday, September 4, 2008

Hanna's Track Shifts Slightly-THIS IS NOT ISABEL

More on Hanna and recent similar storms is posted below. Also, a reminder that this blog is part of my full web site. If you do not see more images at the right here, then click the link above for the full web site.
First, I am thrilled that a lot more of you have taken interest in my blog, but I am amazed how may questions I have gotten about this storm and Isabel. I discussed this earlier in the week- just a few posts back... but I guess I should revisit it again.


  • Isabel reached 150mph winds a few days before landfall-then weakened. The wave memory of that strength is what reached us. Hanna is still a Tropical Storm and only expected to be a minimal Hurricane.
  • Isabel tracked to our south and continued inland- pulling steady south east winds up the bay. Hanna should 'turn the corner', and pass off of the coast. It may clip Ocean City, and looks more like the paths of Floyd('99), and...Charley ('04).
I was an expert witness on a case regarding Isabel, and wrote up a 36 page report describing the unique nature of that storm. The 5 year drought, leading into record snow and very wet seasons. The result was water levels raining 2nd and 3rd all time in many spots- before the storm arrived. Then the track of Isabel itself was extremely rare. It passed north of Cape Hatteras, the point on the map that sticks out on the eastern seaboard. Most often, north of there a storm will encounter the mid latitude Westerlies and turn as a result. Isabel passed north of Cape Hatteras, which allowed that high wall of water- the Storm Surge, to pass unimpeded into the Chesapeake Bay. The track never wavered, and continued northwest up towards Toronto. Flooding was from the surge, not the rain. Check out the path and forecast plots here.

High Tide
Flooding in these storms often comes in two forms.
  1. Down- Rain from the sky.
  2. Up- Storm Surge upon landfall. This is the most destructive.
Despite my confidence and attempt to calm the fear of a repeat, people who live along the water will be watching the high tide and timing of the storm for surge flooding. Bowleys Quarters in Baltimore county seemed to get hit the hardest, I thought I would post their High Tides here. The mid day High Tide on Saturday would be the one of most concern. With the expected track and timing now... the following High Tide early Sunday morning should come with a northwest wind, blowing or draining water out the bay.
Tracking Hanna- Why it Shifted East.
Early this week, I was pumping the track from the National Hurricane Center directly over Baltimore. I tried to make it clear that the the range of time and error would likely bring it close, but not directly on that path. For two straight days, the models I look at were consistently plotting Baltimore. Then it began to show a shift to the south and east. Why?
Weather is all about 'teleconnections'. One storm can be impacted by one or a few others. Or even a ridge of High Pressure such as the one that steered Gustav, but gave us clear skies. As Hanna delayed it's development and turn north an extra day, it allowed the remains of Gustav and the Cold Front to our west to get a little closer to us. Carry this to Saturday, and the steering winds are expected to make Hanna turn north then north east before reaching us.
This GFS plot, compared to the last few days, does show a path over Ocean City on Saturday afternoon. That would sift out winds to more of a Northeast to north direction when the storm gets close. The water level in the bay may run high, but also could drop as this happens as the direction of the wind will help 'push' or 'drain' more water out. This could be counteracted by heavy rain, but definitely different than Isabel. Below are the overnight models and National Hurricane Plot for comparison to the last few days in my previous posts. Beyond that is a comparison to recent storms with the same path- Floyd and Charley.
Computer Models- Spaghetti Plot

Two Storms: Similar Paths, Different Outcomes

While working on a comparison to recent storms with similar tracks, I found two with very different results for Maryland. For starters, it is similar to Floyd, but that was a much stronger storm. At one point, Floyd was on the verge of reaching Category 5 status, and keep pushing from initial threats in central Florida to North Carolina. It was a Tropical Storm when it reach Maryland and passed nearly on top of Ocean City. It was responsible for over 6 inches of rain in Baltimore, 11-13 inches of rain in Annapolis and nearly 20 inches in parts of the Eastern Shore. Ironically, Ocean City had less than 2 inches of rain.Perhaps you remember the images of the town of North East in Cecil County, or Port Deposit at the point where the Susquehanna meets the Chesapeake.

More recently, Hurricane Charley. That came on shore in Florida's Gulf Coast as a Category4, weakened as it crossed into the Atlantic, then hit North Carolina and crossed over Ocean City in a diminished form. By that time, although a similar path to Floyd- no rain fell on the west side of the bay. Quite a contrast.


Anonymous said...

So does this mean when Hanna comes this weekend that it is going to be a Tropical Storm? or no? and are high winds expected? or just alot of rain?

Anonymous said...

Informative! Thank you Justin from the Chesapeake Bay boating community.