Gamma Gone

The relentless shear pounded TD Gamma yesterday, and the depression is no longer being tracked by NHC.



The low level circulation (that swirl in the low cloud in the center bottom-third of the image) is well defined. However, one can see there are no thunderstorms or convection (the colored clouds in this image) near the center. Since one of the requirements for a tropical system is to have convection near and wrapping around the low-level center...NHC doesn't consider this to be a tropical system any longer. It will be monitored for future development, but that seems rather unlikely in this instance.

Gamma should be absorbed by the cold front approaching from the north over the next day or two. That same cold front will make our weather here in Melbourne rather interesting today. Strong winds and thunderstorms are the forecast today, followed by cold stuff... especially Wednesday (fcst hi/lo of 65/45). Keep an eye on the radar today.

Gamma no longer a threat

Long story short...the shear got to Gamma:



This morning, Gamma is estimated to have 40 mph winds...though NHC really isn't sure the winds are even that strong. Movement is a slow northward drift at perhaps 2 mph. Doesn't look like much, does it?

The Weather Service flew the Gulfsteam mission last night. One problem in hurricane forecasting is that the storms are over the oceans, where we obviously don't have many humans launching weather balloons. So, as needed, the NWS will fly a Gulfstream Jet over the ocean and drop instruments from the plane (this time with a parachute, not a balloon) to obtain the measurements, which are fed into the weather prediction models. These Gulfstream obs tell us that the ridge to the north of Gamma in the low levels of the atmosphere is still present, and is stronger than we thought yesterday. Consequently, there is little chance Gamma will head north.

The model forecasts all reflect this, to varying degrees. Since Gamma isn't terribly well defined, model predictions can (and in this case, do) vary, but they are all well south of FL, which is the official forecast. Further, the vertical wind shear is expected to continue, and Gamma is expected to dissipate or be absorbed by an approaching front in the next 3-4 days.

A little better organized, but should pass to our south

Overnight Gamma has not strengthened very much, but seems to have become better organized. Last night's upper-air (weather balloon) data located Gamma's circulation over a greater depth of the atmosphere than previous observations had indicated. Satellite images also support this increased organization. The implication of this is that Gamma will not dissipate quickly or quietly. Gamma has strengthened to maximum winds of 45 MPH, and tropical storm force winds now extend about 100 miles from the center.

The upper-air data also showed a break in the ridge currently to the north of Gamma, giving it an escape route out of the Caribbean. Gamma is currently moving toward the NW at 6 mph, but the turn toward the north and north east should begin over the next day or two. Once Gamma moves far enough north, the effects of the frontal system and upper-level trough of low pressure to the north should turn it quickly toward the north and east.

The official track has shifted south from yesterday's track. The thin black line (yes, I know we're not supposed to focus on the thin black line, but bear with me) now barely grazes the Keys. A number of the global forecast models continue to trap and dissipate Gamma in the Caribbean. Given the apparent increased organization overnight, and the opening of an escape route to the north of Gamma, this seems like an unlikely scenario. The intensity forecast calls for little strengthening during the next three days, which is a downward change from yesterday's forecast. The upper-level wind shear is large and formidable just to the north of Gamma, and will allow little (if any) strengthening.

Effects here will be minimal. Yes, it will rain on Monday, and yes, it will be a little breezy, but there's no reason to board up or stock up right now. Gamma would need to deviate far to the north of the current forecast track (which, of course, could change) for Melbourne to be in any real danger.

Tropical Storms and Christmas Cards

It just seems wrong to be naming tropical storms once the Christmas cards begin flying (we got our first card today). In fairness, I believe we've had a named storm in the Atlantic basin in every month except for April, and in a record setting season such as this, anything is possible.

Gamma has formed this afternoon in the extreme western Caribbean Sea. It is basically in the same neighborhood as Wilma was about a month or so ago. It is not very organized at this time, and is only a minimal tropical storm (40 MPH) as of the 4 PM advisory. Tropical storm force winds do extend outward about 85 miles however. Satellite images over the last few hours show a cloud mass that is weakening (warmer tops in the IR imagry) a little. Gamma is in a high shear environment with a frontal zone to it's north, and the shear is forecast to increase even more over the next few days.

The forecast track is extremely uncertain right now. NHC has drawn a track across Florida that looks a lot like Wilma's track across Florida. It's a little too early to tell if this is the correct track, since the models are in no sort of consensus. This lack of consensus is not surprising; we see this all the time with developing tropical systems. It typically takes the computer models a day or so to really begin to grasp onto a solution. A few of the models weaken and disipate Gamma well south of Florida. Since Gamma is in a high shear environment, and the shear is forecast to increase, weakening to our south is a possibility. The one model that supports the NHC track has a stronger tropical storm (max sustained winds 60 MPH; possible Cat 1 gusts) along that Wilma-like track in the official advisory. Even on this course, since Gamma is a fair bit weaker than Wilma was, it probably will not have a huge effect upon us on Monday. As it stands right now, either of these two solutions are possible.

We finally get respect