I'm just a 23 year old with an ardent passion for weather. I first became aware of this interest after Tropical Storm Isidore struck my area in 2002.
By: KoritheMan , 2:22 AM GMT on August 16, 2012
Tropical Depression Eight
The strong tropical wave we have tracked over the last week or so has finally acquired enough convective organization to be considered a tropical depression. As of the initial advisory from the National Hurricane Center, the following was posted on the tropical cyclone:
Wind: 35 mph, with higher gusts
Location: 29.9°N 55.1°W
Movement: N at 13 mph
Pressure: 1013 mb
An earlier SSMIS overpass just before 0z showed a well-organized inner structure, especially for a system at this latitude. Satellite animations clearly show a much more organized system compared to earlier. Banding features are evident, particularly west and north of the center, and the center itself is generating some relatively cold-topped convection. I've seen colder, but given the high environmental pressures and the nearby dry air, I think the depression is doing well for itself.
Figure 1. Latest infrared satellite image of Tropical Depression Eight. Image credit: NOAA
The cyclone is currently over SSTs near 28C, and underlying water temperatures are expected to remain within the 26C range for about the next three days. A sharp and dramatic increase in westerly shear is forecast, however, is forecast around roughly the same time, which should initiate a weakening trend at longer ranges. This weakening is not expected to be rapid, however, because the cyclone will be accelerating in the same direction as the shear vector. Instead, the shear will primarily help to imbue extratropical transition when combined with cool waters. The SHIPS/LGEM make the system a hurricane in about three days just before the foreseen onslaught of westerly shear. While it is certainly possible that TD Eight will become a hurricane, I am uncomfortable indicating such until I see precisely how the newly-developed tropical cyclone wards off the surrounding dry air. Water vapor imagery shows a small upper low swirling just to the northwest of the depression. However, this feature is not expected to cause an appreciable increase in vertical shear, and it is appears to be outrunning the depression.
The cyclone could become extratropical in about five days. This in good agreement with the global models, which in general show an accelerating extratropical cyclone reaching the Azores early Monday.
Large-scale observations reveal that the depression is well-embedded within high-latitude southerly flow as a large trough amplifies to its west. A secondary trough moving off the east coast of the United States will reinforce the former trough, a pattern which ultimately heralds recurvature. Model guidance is in rather remarkable agreement out to five days, giving high confidence to the track forecast. The 0z model consensus shifted fairly significantly westward. This increases the threat to the Azores, and interests there should closely monitor the progress of this system through Monday. The models do not weaken then post-tropical Gordon all that much on Monday when it is forecast to be lashing the Azores. At that point, it could still be strong enough to bring hurricane force wind gusts to certain areas of the archipelago. I agree pretty strongly with the forecast track from the National Hurricane Center.
5-day intensity forecast
INITIAL 08/16 0000Z 30 KT 35 MPH
12 hour 08/16 1200Z 35 KT 40 MPH
24 hour 08/17 0000Z 40 KT 45 MPH
36 hour 08/17 1200Z 50 KT 60 MPH
48 hour 08/18 0000Z 55 KT 65 MPH
72 hour 08/19 0000Z 60 KT 70 MPH
96 hour 08/20 0000Z 55 KT 65 MPH
120 hour 08/21 0000Z 50 KT 60 MPH...EXTRATROPICAL
5-day track forecast
Figure 2. My 5-day forecast track for Tropical Depression Eight.
The global models continue to suggest the possibility of a tropical depression near the Cape Verde Islands in about 5 days from a tropical wave. Given the time of year and the model consensus, there really is no reason not to expect this.
The GFS has continued to indicate the possibility of development in the western Gulf of Mexico, most likely in the Bay of Campeche. This is forecast to occur in about a week from now from a stalled frontal boundary. Looking at the 500 mb pattern within the global models, any such system would likely move very slowly northwest toward northeast Mexico or south Texas. It takes a lot of deep southerly flow to pull a system out of the Bay of Campeche, especially this time of year.
I remain wholly unenthusiastic about this development.
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