Monday, August 1, 2011

Thoughts on Tropical Storm Emily

This blog post is much more focused towards tropical cyclone interaction with an island/land like Hispaniola. I will touch on my thoughts/instincts on the forecast for TS Emily, but I still need more time to really nail that down. It's not easy! First with Hispaniola...

Tropical Tip: Strong hurricanes (well defined inner core) that moves across land often do not regain their intensity once back over water, while weaker storms intensify much more rapidly once back over the open water. Why? The land disrupts the inner core of the hurricane causing it to weaken, while the outer bands still over water continue to have healthy convection, which will prevent inflow from getting to the surface of the storm once back over open water. A couple good examples of that are Isadore in 2002 and Gustav in 2008.

So how does this apply to Emily and a landmass like Hispaniola? Well, this tip is especially true with a mountainous island like Hispaniola. It really tears up tropical cyclones. However, if Emily can remain fairly weak (not a defined inner core), then it is much more likely (if it can survive its trip across Hispaniola) to ramp up over the open water. If Emily does have a well defined inner core, it will be destroyed by Hispaniola, and it will be very difficult for it to ramp up again. Now of course this doesn't take into account many environmental factors like dry air and shear, as I'm strictly talking about land interaction and its effect on the core of a tropical cyclone. This all assumes the environment is ripe for intensification. That's important to keep in mind.

So here are three possibilities with Tropical Storm Emily:

1) It ramps up fairly quick, steered more by the trough, gaining enough latitude to just miss or clip Hispaniola to the north/east. This would lead to a strong hurricane in the Bahamas, but I believe in this scenario it would get picked up by the trough, barely missing the US. It would be close though!

2) It doesn't ramp up, steered much less by the trough, going across the island of Hispaniola. "If" it survives, then I would expect a decent ramp up until it gets very close to the Florida coast. A Cat-1/2 hurricane is very possible in this scenario, and I would likely expect a US landfall. However, this is still very tricky. It could hit Florida, or just barely miss, eventually hitting/clipping the Carolinas. That would be a forecasters nightmare!

3) It doesn't ramp up initially, but then starts to try to bomb out before moving across Hispaniola. If an inner core was well established, then I wouldn't expect much once it got back into open water. A similar track to #2 would occur, but I wouldn't fear intensification near as much. Of course this just depends on how strong Emily is when it hit Hispaniola. It would probably have to be a strong 1/weak 2, which is a probably unlikely.

So what do I think? I think scenarios 1 and 2 are most likely at this time. I would like to watch it for a day or so to really feel better about it. Since Emily took its sweet time to develop, a more western solution has become apparent. However, this doesn't guarantee that Emily will strike the US or even survive Hispaniola. There is also a chance it could stay very weak and keep moving west/south of Hispaniola. I think that is unlikely, but not impossible by any means. It's just too tough to put out an official track forecast I feel confident about right now. If it would have developed late Saturday/early Sunday, then I would feel confident by now. Since it didn't, I'll wait another day to be as accurate as possible. I'll post more thoughts tomorrow!

*Remember, I'm talking about a well developed inner core that is associated with strong hurricanes, in an environment that is conducive for intensification.

- Well developed core destroyed, very hard to ramp back up. Takes a lot of time...

- Not a well developed core, it will be disrupted, but it will intensify much more readily back over open water...

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