Monday, July 28, 2008

Basins Where Tropical Cyclones Form

Basically, tropical cyclones form all over the world. They form in the north Atlantic, the North-east Pacific, the North-west Pacific, the South-east Pacific (including Australia), the South Indian. and the North Indian Ocean. Although many cyclones (over 30% of the total) many also form elsewhere. In addition,in the Atlantic and north-east Pacific they are called hurricanes, in the north-west Pacific they are called Typhoons, and in all other basins they are simply referred to as cyclones.

Click on image to enlarge it.

All tropical cyclones in the world from 1985-2005. Note the lone tropical cyclone in the South Atlantic in the time period. This had the strength of a Category 2 hurricane at landfall. It was named Cyclone Catarina because it made landfall in close proximity to Santa Catarina, Brazil. It caused approximately 5 fatalities and $400,000,000 worth of damage (wealth adjusted for 2008.)
Image from Wikipedia.

Monday, July 21, 2008

Hurricane Dolly (2008)

Storm Active: July 20-25

Around July 13, a tropical wave formed just east of the Winward islands and tracked slowly through the Caribbean. It was named Tropical Storm Dolly on July 20. Over the next day it crossed the Yucatan pennisula and emerged in the Gulf of Mexico. Dolly intensified rapidly on July 22 and by noon, had 70 mph winds and a minimum pressure of 991 millibars. Dolly kept being upgraded and by noon, Dolly was a Category 2 hurricane with 100 mph winds and a pressure of 964 millibars. By this time, heavy rain along with tropical storm force winds were over parts of Texas and Mexico. Soon after, Dolly made landfall. Over ten inches of rain were dumped locally over the next three days, but eventually, Dolly dissipated. Dolly had caused twenty deaths and $1.5 billion in damage.

Dolly at peak intensity before reaching landfall.

Track of Dolly.

Sunday, July 20, 2008

Tropical Storm Cristobal (2008)

Storm Duration: July 18-23

On July 15, a wave organized west of Florida. But before it had time to develop, it crossed over Florida. It emerged and organized on July 17. Then, very late on July 18, the wave became Tropical Depression Three with 30 mph winds and a pressure of 1009 millibars. On July 19, Tropical Depression Three became Tropical Storm Cristobal just off the coast of Charleston. Shortly after, it became Tropical Storm Cristobal with 45 mph winds and a pressure of 1005 millibars. Cristobal's strength fluctuated over the next few days and stedily moved off the coast but it quickly weakened and became extratropical on July 23.

All times are in Eastern standard time.

Tropical Depression Three shortly before being named.

Track of Cristobal.

Friday, July 4, 2008

Hurricane Bertha (2008)

Storm Active: July 3-20

As July began, a tropical wave moved of the coast of Africa. Unlike many other systems of this region, the circulation remained intact. The wave continued to develop and on July 2, became Tropical Depression Two, with sustained winds of 35 mph and a pressure of 1008 millibars. Then, on the morning of July 3, Tropical Storm Bertha formed. Bertha's winds increased for the first time late on July 3 to 45 mph and the pressure dropped to 1002 millibars. Early on July 4, the track of Bertha shifted to the west, putting the storm closer to Bermuda in a week or so. Then the winds increased to 50 mph, where they would stay for awhile, as Bertha started moving more directly west. Then, during the evening of July 6, Bertha strengthened again into a storm with 60 mph winds and an internal pressure of 998 millibars. Bertha's track now puts it directly into Bermuda. On July 7, Bertha became a hurricane with 75 mph winds and a pressure of 994 millibars. Bertha is now bearing down on Bermuda. Then, Bertha rapidly intensified to a major hurricane and by early July 8, Bertha had reached its peak intensity of 120 mph and a pressure of 952 millibars. After that point, Bertha started to weaken. Also, Bertha turned northward. Then, on July 9, Bertha was downgraded and it only retained minimal hurricane status with 75 mph winds. Overnight, Bertha unexpectedly strengthened to a Category 2 hurricane with 105 mph winds and a pressure of 975 millibars. Also. the track shifted once again putting Bermuda back in danger by Sunday or Monday. Bertha currently has winds of 85 mph. Then over the next few days, Bertha stayed at minimal hurricane status. On July 13, bertha finally weakened to a tropical storm and on July 14 Bertha finally hit Bermuda with 30+ mph sustained winds and gusts above 40. By july 15, Bertha was moving off Bermuda. But a extratropical low moving south-west stopped Bertha and forced in briefly southward. Soon after, Bertha briefly became a minimal hurricane before weakening and becoming extratropical over Iceland.

Bertha as a major hurricane in the central Atlantic.

Track of Hurricane Bertha.

Thursday, July 3, 2008

Typical Hurricane Tracks

In June, systems can form only in a tight region about the Gulf of Mexico and up the east coast.  Near Africa, water is too cold for development.

By July, storms can form farther east in the Atlantic. The Gulf of Mexico, and north of the Caribbean are two hot spots for development.

By August, a tropical system can pop out of nowhere and become a hurricane the next day. Formation has spread to the Eastern most Atlantic and powerful storms are always a possibility in the east Caribbean. Systems are steered in the U.S.A. more often and less turn east than the later season.

The peak of the Hurricane season has come. Except for the extreme north-east, storms can form anywhere in the Atlantic. The official peak of activity is September 11. After this point the hurricane season starts to decline.

In October, temperatures of the east Atlantic drop below favorable for hurricanes. Activity can still be found in the Caribbean, but is much more common north of that area, including the Gulf of Mexico. Powerful major hurricanes are uncommon from this point on.

From November to the new year, Caribbean storms are almost non-existent. The cooling waters hinder almost all development. Most, if not all storms form and dissipate in the open waters way off the coast of the U.S.

All photos provided by National Hurricane Center.