Miriam Hits Cat 3 Strength off of Mexico; Jelawat a Cat 4 Super Typhoon

In the Eastern Pacific off the coast of Baja Mexico, Hurricane Miriam put on a burst of rapid intensification this morning that has brought it to Category 3 strength with 120 mph winds. This makes Miriam the 2nd strongest Eastern Pacific hurricane of 2012 behind Hurricane Emelia of July, which hit Category 4 strength with 140 mph winds. Satellite imagery shows that Miriam has a tiny "pinhole" eye, and continues to intensify. Miriam could approach Category 4 strength before an eyewall replacement cycle begins early Tuesday. High wind shear will attack Miriam late this week, and our two top models, the GFS and ECMWF, show Miriam hitting central Baja as a weak tropical storm on Friday or Saturday, with moisture from the storm streaming into Arizona and New Mexico by Sunday.


Figure 1. Morning satellite image of Hurricane Miriam.

Super Typhoon Jelawat the 2nd strongest tropical cyclone of 2012
In the Western Pacific, Super Typhoon Jelawat put on a remarkable burst of rapid intensification on Sunday, strengthening from a tropical storm with 65 mph winds to a Category 4 typhoon with 140 mph winds in just 24 hours. Jelawat has topped out as a Category 4 super typhoon with 150 mph winds, making it the 2nd strongest tropical cyclone on Earth so far in 2012, behind Super Typhoon Sanba (175 mph winds.) Jelawat is located about 200 miles to the east of the Philippine Islands, and the storm's outer spiral bands are bringing some moderate rains to the eastern Philippines. Wind shear is a light 5 - 10 knots, and Jelawat is over very warm ocean waters of 29°C. These warm waters extend to great depth, resulting in a total ocean heat content of over 100 KJ/cm^2, which is exceptionally high. These conditions should allow Jelawat to maintain major typhoon status for at least three more days. Satellite loops show an impressive, well-organized typhoon with a large symmetric area of heavy thunderstorms with cold cloud tops.

Jelawat is expected to move slowly to the north-northwest to northwest, roughly parallel to the Philippines, through Tuesday. After that, there remains major uncertainty on where Jelawat might go, with the spread in the computer models about 400 miles for the 3-day forecast. The official Joint Typhoon Warning Center forecast compromises between the unusually large spread in the models, predicting a path well east of the Philippines and Taiwan. However, our two top models--the GFS and ECMWF--both predict that Jelawat will hit Taiwan, and the ECMWF model predicts that Jelawat will also graze the northern portion of the Philippines' Luzon Island. Given the large spread in models, the 3 - 5 day forecast for Jelawat is low-confidence, and residents of Luzon and Taiwan should not assume that Jelawat will miss them.


Figure 2. MODIS satellite image of Jelawat taken at 12:30 am EDT Monday, September 24, 2012. At the time, Jelawat was a Category 4 storm with 145 mph winds. Image credit: NASA.

Pesky Nadine still out there
Persistent Tropical Storm Nadine continues to wander westwards in the Middle Atlantic, far enough south of the Azores Islands that those islands will see only very sporadic rain showers over the next few days. Nadine will likely turn to the north over the middle Atlantic late this week, but will still probably be around a week from now. The storm is not likely to threaten any land areas for at least the next seven days.

GOES-13 satellite outage
The imaging instrument on NOAA's geostationary satellite that provides regular images every 15 minutes for the Eastern U.S. and Atlantic Ocean, GOES-13, has been experiencing an increasing amount of noise in the signal since September 12. The noise got so bad on Sunday night that the instrument was placed in stand-by mode, and engineers are attempting to troubleshoot the problem. GOES-15, the geostationary satellite that covers the Western U.S. and Eastern Pacific, is now taking images of all of North America to help compensate. However, there is no regular 15-minute satellite imagery available for most of the North Atlantic, including the Caribbean. September is a bad time to be without satellite imagery over the Atlantic, but fortunately, there are not any threat areas in the Atlantic we are currently worried about. The CIMSS Satellite Blog has more information on the outage, and also has links to polar orbiting satellite imagery over the region where we do not have geostationary data. The loss of GOES-13 data will degrade the accuracy of the computer forecast models for the globe, particularly over the Atlantic, for the duration of the outage.

Jeff Masters