WunderBlog Archive » Category 6™
Category 6 has moved! See the latest from Dr. Jeff Masters and Bob Henson here.Gert and Franklin
Tropical Storm Gert formed last night, marking the earliest hurricane season ever to have seven named storms. The previous record year was 1936, when the seventh storm formed on August 7. Gert has warm water underneath and good outflow above, but not enough room to do much intensification. A look at the latest SST plot for the Gulf of Mexico shows the warm 29 - 30C water in the southern Gulf under Gert, and also the cold water wake of Hurricane Emily.
The winds of slow-moving Category 2 and higher hurricanes often stir up cooler water from deep below the ocean surface, cooling the surface waters in their wake by 1 - 3C or more. However, the winds of Gert are only 40 mph, and not likely to produce a cold water wake of their own. The sudden stoppage of Emily's cold water wake just before the coast of Mexico south of Brownsville is an artifact of the technique used to make the SST map--data from more than one day is combined. The plot says data from 7/19 through 7/21 were used, and Emily hit Mexico on July 20, so undoubtedly the data near the coast where Emily hit came from July 19, before the storm crossed the coast. The reason multiple days are used to generate these composites it that the satellite making the measurement needs cloud-free conditions to be able to measure the sea surface temperature. The area near the coast of Mexico was no doubt cloud covered on July 20 and 21, so data from July 19 was used. The reason no cold water wake is seen from where Emily approached the Yucatan as a Category 4 hurricane is probably because the storm was moving too quickly to stir up much cold water from down deep. Emily's forward speed was 20 mph then, and slowed down to zero when it approached Brownsville.
Turning our attention to Tropical Storm Franklin, we see a classic example of a sheared system. The low-level center of rotation is almost completely exposed, with just one glob of thunderstorms clinging to the storm's south side. Strong upper level winds blowing from the northwest are ripping away any convection that tries to fire up on the north side of Franklin. The shear is expected to continue for at least the next day, and Franklin should continue heading out to sea and probably weaken further.
Out in the rest of the tropics, nothing eye-catching is happening today, so we may be in for a quiet week for a change!
Jeff Masters
The winds of slow-moving Category 2 and higher hurricanes often stir up cooler water from deep below the ocean surface, cooling the surface waters in their wake by 1 - 3C or more. However, the winds of Gert are only 40 mph, and not likely to produce a cold water wake of their own. The sudden stoppage of Emily's cold water wake just before the coast of Mexico south of Brownsville is an artifact of the technique used to make the SST map--data from more than one day is combined. The plot says data from 7/19 through 7/21 were used, and Emily hit Mexico on July 20, so undoubtedly the data near the coast where Emily hit came from July 19, before the storm crossed the coast. The reason multiple days are used to generate these composites it that the satellite making the measurement needs cloud-free conditions to be able to measure the sea surface temperature. The area near the coast of Mexico was no doubt cloud covered on July 20 and 21, so data from July 19 was used. The reason no cold water wake is seen from where Emily approached the Yucatan as a Category 4 hurricane is probably because the storm was moving too quickly to stir up much cold water from down deep. Emily's forward speed was 20 mph then, and slowed down to zero when it approached Brownsville.
Turning our attention to Tropical Storm Franklin, we see a classic example of a sheared system. The low-level center of rotation is almost completely exposed, with just one glob of thunderstorms clinging to the storm's south side. Strong upper level winds blowing from the northwest are ripping away any convection that tries to fire up on the north side of Franklin. The shear is expected to continue for at least the next day, and Franklin should continue heading out to sea and probably weaken further.
Out in the rest of the tropics, nothing eye-catching is happening today, so we may be in for a quiet week for a change!
Jeff Masters
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.