John crunches Baja; two Atlantic systems to watch

Hurricane John crunched ashore the eastern side of Mexico's Baja Peninsula last night at 5pm PDT as a Category 2 hurricane with 110 mph maximum winds. The east side of the Baja Peninsula is relatively sparsely populated, and John largely spared the resort towns of Cabo San Lucas and San Jose del Cabo. Radar from Guasave shows John is moving up the Baja Peninsula, and is now battering the capital, La Paz, as a Category 1 hurricane. John will continue to weaken as it moves northwest along the Baja Peninsula, and should die before it reaches the U.S. However, moisture from the hurricane will likely bring flooding rains to portions of the Southwest early next week.


Figure 1. Radar from Hurricane John at landfall, 8:38pm EDT Friday 9/1/06. Image credit: Servicio Meteorologico Nacional of Mexico.

NHC declares a new "invest" on tropical wave in Lesser Antilles
The tropical wave surrounded by a cloud of African dust and dry air that I've been commenting on ever since it left the coast of Africa, is now an official threat. NHC has designated this wave "Invest 99L" this morning. The wave is near 15N 61W, right on top of the Lesser Antilles Islands. It is surrounded by a large cloud of dry air and African dust, but has slowly been able to pump more moisture into its center each night over the past few days as thunderstorm development kicks up then dies away. The thunderstorm activity has picked up considerably this morning, the first time the disturbance has been able to build thunderstorms during the daytime hours. The disturbance is tracking west at 15 mph into a large upper trough of low pressure over Cuba and Hispaniola that is creating about 10-20 knots of shear over 99L. The trough is expected to weaken and move west over the next few days, potentially creating a low shear environment over most of the Caribbean. This could allow intensification of 99L into a tropical depression by Monday.


Figure 2. Preliminary model tracks for Invest 99L. These models are described at the NHC web site.

The mid-Atlantic tropical wave to watch
A tropical wave near 11N 39W, midway between Africa and the Lesser Antilles Islands, was declared "Invest 98L" last night by NHC. However, the wave no longer has a well-defined low level circulation. Instead, this disturbance has a long oval area of circulation extending across 10 degrees of longitude, from about 33W to 43W, as seen in a QuikSCAT satellite pass from 4:11am EDT this morning. The heaviest thunderstorm activity has shifted eastward several hundred miles since last night, from 40W to about 35W. It appears that if this disturbance develops, it will happen from this more easterly position. The model runs from last night and this morning (Figure 3) all used the more westerly position of 40W, so can be disregarded. The system is moving slowly west at 10 mph, and could be near or north of the Lesser Antilles Islands on Thursday. Wind shear over the system is low, 5-10 knots, and the wave is over warm SSTs of 83-86F (28.5-30 C). Wind shear is forecast to remain low over the next few days, and the system has the potential to become a tropical depression by Monday. A modest inhibiting factor might be the large area of dry air and African dust to the wave's north.


Figure 3. Preliminary model tracks for Invest 98L. These models are described at the NHC web site.

New wave coming off the coast of Africa
A strong new tropical wave is emerging from the coast of Africa today near the Cape Verde Islands. Some of the computer models continue to develop this wave into a tropical storm or hurricane by the middle of next week.

Which of these three waves should most concern us? Both the wave coming off Africa today and the one in the middle of the Atlantic--98L--will probably end up recurving out to sea. However, 99L is already in the Caribbean and is forecast to enter a low shear environment, so this is the one to be most concerned with.

Dr. Gray's September 1 forecast
The hurricane forecast team at Colorado State University headed by Phil Klotzback and Dr. Bill Gray issued their September forecast for Atlantic hurricane activity today. They predict 5 named storms, 3 hurricanes, and 2 intense hurricanes for September, which is about normal for that month. They predict an additional 2 named storms and one hurricane in October, and one named storm in November. This would give the hurricane season of 2006 total of 13 named storms, 5 hurricanes, and 2 intense hurricanes. An average season has 11 named storms and 6 hurricanes. They credited dry air from the Sahara and more El Nino-like conditions than expected for the lower than average hurricane activity observed in August. Prices of oil, natural gas, and heating oil futures fell on commodity markets by 1-3% on the news of the forecast. The Klotzbach/Gray team originally forecast that 17 named storms would form this year.

Typhoon Ioke
Typhoon Ioke is now not even a Category 4 storm, having weakened a to mere strong Category 3 typhoon with 125 mph winds. It still has a chance to re-strengthen to a Category 4 in the next few days, before increasing wind shear and cooler waters will permanently take it out of Category 4 territory.

Next update
I'll have an update Sunday morning, unless there's some major development today to report.

Jeff Masters