| SOMETCUBA Bulletin |
Volume 6 Number 1 |
January 2000 |
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CYCLONE SEASON OF 1999 ON THE NORTH ATLANTIC OCEAN
Main characteristics of the 1999 cyclone season
The 1999 cyclone season was an active one, both in the amount of organisms that reached the rank of tropical storm (12) and the amount of these that became hurricane (8). Amongst the main factors that contributed to the active nature of this season, the following can be mentioned:
The predominance of easterly winds in the high tropical troposphere, related to the cooling of the water on the eastern equatorial Pacific Ocean.
The western phase of the winds in the equatorial stratosphere and.
The warming of the water on the tropical Atlantic Ocean during this period (Ballester et al., 2000).
A total of 16 tropical depressions originated in 1999, a figure that equates the historical mean (considering the series between 1967 and 1998). 75% of these depressions surpassed this category, which is above the historical mean of 60% for the Atlantic Ocean. 62% of depressions originated from tropical waves. On Table 1 the classification of tropical cyclones on the Atlantic Ocean, according to the intensity of maximum sustained winds at the surface is presented.
Table 1. Classification of tropical cyclones on the Atlantic Ocean, according to the intensity of maximum sustained winds at the surface.
Clasification
Maximum Sustained Winds. Km./h(Averagw over one minute)
Tropical Depression £ 62
Tropical Storm 63 – 117
Hurricane
³ 118
The number of 12 cyclones developed over the north Atlantic equates the five-year period of 1995-1999 with that of 1932-1936 with a total of 65 tropical storms, while the amount of 8 hurricanes places it as the most active since 1886, with 41 hurricanes. Amongst these eight hurricanes, five were intense (category 3 or above on the Saffir-Simpson scale, see Table 2) Bret, Cindy, Floyd, Gert and Lenny reached all category 4, standing out Floyd with maximum wind speed of 250 Km/h and a minimum pressure of 921 hPa.
A remarkable fact of the 1999 season was the direct affectation by at least some organism to the United States and several other countries around the Caribbean Basin. The U. S. suffered the effects of Bret, Dennis, Floyd, Harvey and Irene. The Bahamas were directly hit by Floyd; The Leeward Islands by Jose and Lenny. Central America by Katrina and Cuba by Irene. The cyclone that greatest looses caused, both in human lives and economic damage was the intense hurricane Floyd.
Table 2. Classification of hurricanes according to the Saffir – Simpson scale
Category
Central Presure (hPa)
Maximum Sustained Winds(Km./h)
Damage
1
³ 980
118 – 153
Minimum
2
965 - 979
154 – 177
Moderate
3
945 - 964
178 – 209
Extensive
4
920 – 944
210 – 250
Extreme
5
< 920
> 250
Catastrophic
As the monthly tropical storm formation distribution shows on Table 3, the months of August and October stand out with 4 and 3 organisms respectively, figures that surpass the mean values determined for the period 1886-1998. An interesting fact for the month of November is the presence of an intense hurricane on the Caribbean Sea, originated in this area, such event didn’t occur in this month since 1912.
Table 3. Mean monthly frequency of tropical cyclones for the period 1886-1998 and behavior on 1999.
Period
June
July
August
September
October
November
1886 – 1998
0.5
0.7
2.1
2.8
1.8
0.4
1999
1
0
4
3
3
1
The most active period was bracketed between the 18 of August and the 19 of September with the formation of seven tropical storms and tropical depression No. 7.
Table 4 shows a summary of the characteristics of tropical cyclones developed on 1999 over the Atlantic basin, while trajectories are shown on Figure 1. This figure shows that two tropical cyclones developed over the Gulf of Mexico (Bret and Harvey), three over the Caribbean Sea (Irene, Katrina and Lenny) and the remaining seven over the Atlantic Ocean. Out of those seven, only Jose influenced over the islands of the Caribbean Sea. Quite relevant among all trajectories is that followed by Hurricane Lenny over the Caribbean Sea, with a marked course to the east at quite low latitude. This is seen by the first time since 1871.
Individual
characteristics of tropical cyclones on 1999
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