Tropical Trouble

IR Satellite / Courtesy: WeatherTap

Hurricane season isn’t over yet! A tropical wave in the Caribbean has garnered meteorological attention in the last several days. It’s not terribly impressive currently but our computer models do strengthen the system quite a bit by the end of the upcoming week.

Most models (GGEM, GFS, Euro) show this wave intensifying slowly through the next 96 hours with gradually lowering surface pressures. Something happens after 96 hours on the models, however, that results in a rather sudden strengthening. So what is the something?

Here’s the 114 hour op GFS dynamic tropopause pressure forecast. Notice the cyclonic potential vorticity anomaly over the eastern Gulf of Mexico and the northwest Caribbean Sea. It appears that a PV streamer breaks off from the westerlies early this coming week and dives into the Gulf and Caribbean. The baroclinic assist from this PV streamer is what the models key in on to really let this system take off.

While it may seem counter-intuitive that a baroclinic upper level system is able to jump start TC genesis it actually occurs with a fair amount of regularity, particularly in the early and latter parts of a tropical season. This forecast PV anomaly also enables a large and impressive outflow channel to develop for the TC with a developing downstream ridge.

The always comical GGEM has some interesting weather-porn with what may become Sandy.

180 hour 12z 10/20 GGEM theta/wind on 1.5 PVU Surface

The deep, negatively tilted trough absorbs TC Sandy from the Atlantic and hurls it into the east coast of the U.S.

180 hour 10/20 GGEM Forecast

No one wants this solution to verify! Thankfully, the GGEM is notorious for these funky and far-out solutions. There’s not an October that goes by that the GGEM doesn’t have Hazel part 2 slamming into the Mid Atlantic.

The more likely scenario is TC Sandy sends some moisture back toward the U.S. as the big trough digs through the Great Lakes next weekend and becomes negatively tilted like the Euro shows. Another solution is that the the system moves harmlessly out to sea like the GFS shows. Both of these aforementioned possibilities are exponentially more likely than the GGEM fantasy ‘cane.

But since we’re on the topic of Hazel – what did the synoptic setup for Hazel look like? Wow.

20th Century Reanalysis for Hurricane Hazel (10/15/1954 12z) / Courtesy: ESRL PSD

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One thought on “Tropical Trouble

  1. Pingback: What a (Forecasted) Storm! | Way Too Much Weather

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