Ernesto near hurricane strength

Tropical Storm Ernesto is near hurricane strength, headed for a landfall near the North Carolina/South Carolina border this evening. The latest center report from the Hurricane Hunters at 3:37pm EDT found a central pressure of 991 mb, just 1 mb higher than Ernesto's pressure when he was a hurricane south of Haiti. Radar animations from the Wilmington radar don't show an eyewall forming yet, put the intensity and number of spiral rain bands is increasing. Again, it is a good thing Ernesto has only a few hours over water to intensify, or this would have been a Category 2 hurricane in another day. The latest surface wind measurements from the SFMR instrument carried on NOAA's P-3 aircraft found highest winds of 67 mph, on the southeast side of the storm (Figure 1). Wind observations from offshore buoys have been as high as 42 mph sustained with gusts to 50 mph this afternoon. Rainfall amounts up to 8 inches have been estimated from Wilmington radar in some small pockets, and amounts of 4 inches are common across North and South Carolina. An additional 4-8 inches will fall over much of North Carolina, making fresh water flooding the main hazard of the storm. A storm surge of up to 5 feet near the coast will also cause some problems.


Figure 1. Wind analysis of the NOAA P-3 Hurricane Hunter data from 3:30pm EDT 8/31/06.

Ernesto is under wind shear of 10-20 knots, thanks to southwesterly upper-level winds from the trough of low pressure pulling the storm to the north. This shear is keeping the storm from organizing as quickly as it would otherwise. Water temperatures under the storm are about 30 C, which is very favorable for intensification. The eastern portion of the storm is over the axis of the very warm Gulf Stream Current.

Hurricane John
The Air Force Hurricane Hunters reached Hurricane John this afternoon, and ofund that it had weakened to a Category 2 hurricane. This probably occurred because of interaction with the mountainous terrain of Mexico. However, John is now pulling away from the coast of Mexico, and may be able to re-intensify. The forecast track of the storm takes it very near to the tip of the Baja Peninsula, and John could be the strongest hurricane to affect Baja since Hurricane Liza of 1976 brushed the peninsula as a Category 4 storm. Wind shear is light and forecast to remain low, and sea surface temperatures (Figure 2) are a very warm 30 C under the hurricane--about 1-2 degrees C above normal for this time of year. John's strength is likely to be controlled by difficult to predict eyewall replacement cycles over the next two days.


Figure 2. Current sea surface temperatures along the Pacific coast. Temperatures in the Gulf of California may not be accurate, due to difficulties retrieving the temperature via satellite measurements in such a narrow body of water. The red line separating blue colors from yellow marks the 26 C isotherm--the critical temperature needed to sustain a tropical cyclone. Note the very cool waters extending from the California border southwards along the coast. This long stretch of cool water will make it difficult for John to hold together if it tries to approach California. Image credit: NOAA/AOML.

Is John a threat to the U.S.?
In yesterday's blog, I discussed in detail the historical record of the five Eastern Pacific tropical cyclones that have affected the U.S. with tropical storm force winds. The latest model guidance and official forecast now suggest that the U.S. is not at risk from John.

Super Typhoon Ioke
Super Typhoon Ioke hit tiny Wake Island with the left side of its eyewall this morning. A storm surge of 8 feet with 50 foot waves probably battered the island. Observations from Wake showed winds of 78 mph gusting to 100 mph and a pressure of 934 mb before the instrument failed at 2:18am EDT this morning. A drifting buoy (52609) about 100 miles east of Wake apparently took a direct hit, and measured a pressure of 921.5 mb in the eye:

Measurements from drifting buoy 52609:

Date/Time Pressure
-------------------
8/30/06 16 995.9
8/31/06 00 970.5
8/31/06 02 939.6
8/31/06 03 921.5
8/31/06 05 936.7
8/31/06 06 951.7

Unfortunately, the buoy has no wind measurement equipment. Ioke continues to be a borderline Category 4/5 super typhoon, and is not expected to decline to category 3 strength for several more days. This would probably make it the longest-lived Category 4 or higher storm on record anywhere.

African tropical waves
The tropical wave near 18N 50W is surrounded by a large cloud of dry air and African dust and has lost almost all of its thunderstorm activity near the center. Development is not likely until Sunday at the earliest, when it may find a moister environment near the Lesser Antilles Islands.

A tropical wave near 12N 36W, 700 miles southwest of the Cape Verde Islands, has shown a small increase in thunderstorm activity today. Some slow development of this system is possible over the next few days.

A spinning area of clouds few hundred miles north of Puerto Rico is associated with an upper level low pressure system. Development is not expected of this system.

All of the global models are calling for development of a tropical wave that wil come off the coast of Africa this weekend. The models are not very good at forecasting development of tropical systems coming off the coast of Africa; it will be interesting to see if this consensus forecast is correct.

Next update
Tonight, I'll be talking live at 8:45pm EDT on the Barometer Bob show:

http://www.barometerbobshow.com/

Jeff Masters