A Jelawat mystery; moisture associated with TS Norman drenching Texas

Powerful Typhoon Jelawat is hammering Japan's Ryukyu Islands as the typhoon steams northeastwards towards Okinawa at 12 mph. Jelawat has weakened to a Category 3 storm with 125 mph winds, thanks to an eyewall replacement cycle and an increase in wind shear to a high 20 - 30 knots. At 7 pm local time, the winds today at Shimoji Shima Island were 66 mph, gusting to 85 mph. Jelawat has dumped 308.5 mm (12.1") rain in 12 hours at Tarama Airport. Satellite loops and radar loops show an impressive, well-organized typhoon with a 33 mile-wide eye, and a large, symmetric area of heavy thunderstorms with cold cloud tops.

The models are in close agreement that Jelawat will pass over or very close to Okinawa, Japan, as a Category 2 or 3 typhoon on Saturday, between 03 - 06 UTC. Jelawat could hit the main island of Honshu in Japan as a tropical storm or Category 1 typhoon on Sunday. Wind shear will continue to increase over Jelawat for the remainder of its life, causing a steady weakening of the storm.


Figure 1. Radar image of Typhoon Jelawat over Japan's southern Ryukyu Islands at 11:05 pm local time on September 28, 2012. Image credit: Japan Meteorological Agency.

A Jelawat mystery
Jelawat has had a classic appearance on satellite imagery during its long stint as a Super Typhoon, with a large symmetric eye surrounded by intense thunderstorms with very cold cloud tops. However, at two points in its life--for several hours on September 25 (Figure 2), and again near 08 UTC September 27--both visible and infrared satellite images showed a very odd boundary extending north-northwestwards from the northeast side of the eye for about 50 miles. I've never seen any such feature in a tropical cyclone, and am a loss to explain what is going on. The typhoon was not close enough to any land areas for this to be a topographic effect, and there wasn't any obvious dry air or significant wind shear that could have caused a perturbation like this.


Figure 2. High resolution visible (left) and infrared (right) satellite imagery of Super Typhoon Jelawat from the new Suomi VIIRS instrument, taken at 0431 UTC on September 25, 2012. At the time, Jelawat was a Category 5 storm with 160 mph winds. A very odd line appears along the north side of the eye. Image credit: Dan Lindsey, Colorado State University.
Brian Tang

Nadine a hurricane again
Non-stop Nadine has regenerated to hurricane strength again, as the long-lived storm enters its 16th day of life. Nadine is not expected to be a threat to any land areas for the next seven days, but moisture associated with Nadine has flowed eastwards over Spain, bringing heavy rains and flooding problems. The GFS model shows Nadine getting caught up in a trough of low pressure on Wednesday and lifted to the northeast over colder waters, where it would likely die. The 00Z run of the ECMWF model predicts that Nadine will hang around an extra two days, finally getting pulled northeastward over cold waters next Friday. Nadine is already in eighth place for longest-lived named storm since 1950, according to a list compiled by Dr. Phil Klotzbach of Colorado State University:

1) Ginger, 1971: 21.25 named storm days
2) Carrie, 1957: 19.5 named storm days
3) Alberto, 2000: 19.25 named storm days
4) Bertha, 2008: 17 named storm days
5) Inga, 1969: 17 named storm days
6) Kyle, 2002: 16.75 named storm days
7) Inez, 1966: 16.25 named storm days
8) Nadine, 2012: 16.0 named storm days

The all-time record is held by the San Ciriaco Hurricane of 1899, which had 28 named storm days.


Figure 3. MODIS satellite image of Tropical Storm Nadine taken at 8:30 am EDT Friday, September 28, 2012. At the time, Nadine had top winds of 70 mph, and would be declared a hurricane 3 hours later. Image credit: Navy Research Lab, Monterey.

Tropical Storm Norman forms near Baja, Mexico; associated moisture feeding heavy rains in Texas
Tropical Storm Norman has formed this morning near the tip of Baja, Mexico, and promises to be a potent rain-maker for Mexico and the Southern U.S. Norman's moisture will feed the formation of an extratropical storm that will form in South Texas on Saturday. The storm's center will potentially move over the Northern Gulf of Mexico on Sunday and Monday, but the storm will probably not have enough time over water to convert to a tropical system. The storm will bring heavy flooding rains to Texas, Louisiana, Mississippi, Alabama, and the Florida Panhandle Saturday through Monday. Flooding has already been observed in West Texas this morning. Midland-Odessa picked up 3.12” of rain so far today, making it the 3rd wettest September day on record. The wettest day in city history is August 24th, 1934, when 5.32” fell.


Figure 4. Predicted rainfall totals for the 5-day period ending at 8 am EDT Wednesday, October 3, 2012. Moisture from the Eastern Pacific's Tropical Storm Norman is expected to surge eastwards and bring heavy rains to much of Texas and the North Gulf Coast. Image credit: NOAA/Hydrometeorological Prediction Center.

New African wave may develop next week
A tropical wave expected to move off the coast of Africa on Sunday will develop into a tropical depression by next Wednesday, predicts today's 06Z run of the NOGAPS model. The wave is predicted to recurve to the north more than 1,000 miles east of the Lesser Antilles Islands.

Jeff Masters