Here Comes Joyce

Forecast track for TD Ten – soon to be TS Joyce – valid 11AM EDT August 22.

Tropical Depression Ten formed in the Atlantic this morning and is forecast to quickly strengthen into a tropical storm.  At that point (probably tonight or early tomorrow), it will receive the name Joyce.  As you can see from the image above, TD Ten is not forecast to strengthen beyond a tropical storm in the next five days, nor is it expected to pass over or very near any land masses during that time.  Of course, as with Isaac, any forecast track contains errors and it’s possible the track of soon-to-be Joyce will change to be in line with some land in the future.  Right now, though, no land is even contained within the error domain of the forecast track.

Speaking of errors in the forecast track, let’s take a look at why I continue to stress patience when a storm is far out to sea.

GFS ensemble tracks for TS Isaac from the 06Z run of the GEFS model. Each of the 20 members is run out to 240 hours (10 days).

The 20 runs of the GFS ensemble model produced a wide range of forecast tracks for Tropical Storm Isaac.  On one end, Isaac stays off the East Coast of the US and turns out into the Atlantic without ever making landfall on the US mainland.  On the other end, Isaac goes out into the Gulf of Mexico and makes landfall as far west as New Orleans.  (I’m not going to entertain that option right now.)  If you were to look at all the hurricane/tropical models, you would find solutions ranging from landfall at Wilmington, NC to Isaac merely dissipating in the Caribbean Sea.

Overall, the official forecast track from the NHC has shifted slightly westward today in response to the cluster of model solutions shifting in that direction.  The reality is that the forecast track will likely shift several times over the next few days as Isaac gets closer to the US.  For this reason, serious concern over a US landfall should wait until the end of this week when we should have a better idea of Isaac’s track.

The other issue with Isaac is the intensity forecast.  Isaac is expected to strengthen into a hurricane before passing over Hispaniola and Cuba.  As it does so, it is expected to weaken and return to tropical storm strength before exiting Cuba and re-intensifying over open waters.  In other words, it looks like a roller coaster ride for Isaac over the next week.  The exact changes in intensity will be determined by how much time the center of Isaac spends over land.  There are 10,000 foot mountains in the Dominic Republic that would significantly weaken Isaac if it passed over that area.  (Unfortunately, the 10,000 foot mountains would also enhance the rainfall from Isaac and lead to flooding and mudslides.)  On the other hand, if Isaac’s track were to shift a little south, it could spend much more time over open water and strengthen even more than forecast.

The bottom line on Isaac is there’s a lot of uncertainty at this point and we’ll need to follow any changes closely over the next few days.

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