HURRICANE SEASON OF 1998 IN THE NORTH ATLANTIC

General characteristics of the Hurricane Season of 1998

The Hurricane season of 1998 was a very active one, not only in the total number of organisms that reached the rank of tropical storm (14), but also in the amount of these that turned into hurricanes (10). A review to the Climatology of Tropical Cyclones since 1886 shows that a similar amount of organisms with intensity equal or above 63 km/h (lower limit to classify as a tropical storm, see table 1) has occurred before in 1916, 1953 and 1990, while a greater activity has occurred five times, standing out the season of 1933 with 21 tropical storms.

One of the factors that contributed to the active behavior of this season was the quick cooling of waters in the eastern Equatorial Pacific Ocean occurred after the weakening in June of the strong ENSO event in place since 1997.

Table 1. Classification of Tropical Cyclones attending to the intensity of maximum sustained winds on the surface.

Classification	Maximum sustained wind in km/h (mean for 1 min.)
tropical depression tropical storm hurricane	£ 62 63 – 117 ³ 118

As an average for the Atlantic Ocean, 60% of tropical depressions in one season reach a higher category (considering a series from 1967 to 1997). In this year all tropical cyclones originated in the Atlantic basin surpassed the stage of tropical depression, this is the second time it happens in the statistical records. The first time it was in a recent date, 1996. It’s also interesting to point out that 65% of all organisms originated from tropical Waves, which is totally normal for this zone of the Planet.

The amount of ten hurricanes in a season equals that of seasons from 1887, 1893 and 1933 and was surpassed by those from 1916, 1950 and 1995 with 11 and 1969 with 12.

The sum of 33 hurricanes since 1995 places this four years period as the most active since 1886.

Out of these ten hurricanes, three were intense (Category 3 or higher in the Saffir–Simpsom scale, See table 2), a figure quite behind the record of 8 intense hurricanes for a single season reached in 1961.

Bonnie, Georges and Mitch were the three hurricanes that reached the highest intensity, standing out amongst them Hurricane Mitch that reached maximum sustained winds (mean in one minute) of 287 km/h and a minimum pressure of 905 hPa. This placed it together with Hurricane Camille (August 1969) as the fourth most intense of this century.

Table 2. Classification of hurricanes according to the Saffir-Simpson scale.

Category	Central pressure (hPa)	Maximum sustained wind (km/h)	Damage
1 2 3 4 5	980 965 – 979 945 – 964 920 – 944 < 920	118 – 153 154 – 177 178 – 209 210 – 250 > 250	Minimum Moderate Extensive Extreme Catastrophic

A significant fact from the 1998 hurricane Season was that the U. S. and almost all Countries from the Caribbean basin were affected by some organism. States adjacent to the coast of the Gulf of Mexico suffered one way or another the effects of Charley, Earl, Frances, Georges, Hermine and Mitch while the eastern coast was affected by Bonnie. Over the countries of the northern group of the Lesser Antilles crossed Hurricane Georges causing a considerable amount of human and material loses, mainly in the Dominican Republic and Haiti. Central America suffered one of the greatest tragedies registered in the last two centuries due to hurricane Mitch, which since it’s formation produced intense rainfall with great flooding over the area causing 11,000 deaths and economic damages assessed in over 3,500 millions of dollars.

As we watch the distribution of formation per months, September and August stand out with 6 and 4 organisms respectively, figures that surpass the historical averages for the period 1886- 1997 (See Table 3)

Table 3. Historical average of Tropical Cyclones and behavior in 1998

	Jun.	Jul.	Aug.	Sep.	Oct.	Nov.
Average (1886 – 1997)	0.5	0.7	2.1	2.8	1.8	0.4
1998	0	1	4	6	2	1

The most active period was bracketed between August 19^th and September 30^th with the formation of ten cyclones. During September 25^th and 26^th four hurricanes were visible at the same time, a completely unusual fact for the Atlantic basin that occurs for the first time this century.

A general resume of the characteristics of tropical storms and hurricanes originated during 1998 over the Atlantic basin is shown in Table 4, while the trajectories of these organisms can be seen in Figure 1. Here it shows that four tropical cyclones originated in the Gulf of Mexico (Charley, Earl, Frances and Hermine). Only one, Mitch "was born" on the Caribbean Sea and the remaining nine did it over the Atlantic, from them, only Georges entered the Caribbean Sea.

Altogether, tropical cyclones this season were responsible for 11,629 deaths while economic damages are estimated in little above 4,350 millions of dollars.

Fig.1 Trajectories of Tropical Cyclones on the 1998 season.

Table 4. Some characteristics of Tropical Cyclones registered during 1998

Name	Birth Date	Ending Date	Maximum Winds (km/h)	Minimum Pressure (hPa)	* UTC Date and Time of maximum intensity	Saffir-Simpson Scale
Alex	07/27	08/02	85	1000	07/30 18	--
Bonnie	08/19	08/30	185	954	08/24 00	3
Charley	08/21	08/22	95	1003	08/22 06	--
Danielle	08/24	09/03	165	965	09/01 18	2
Earl	08/31	09/03	160	986	09/03 00	2
Frances	09/08	09/12	105	991	09/11 06	--
Georges	09/15	09/29	240	937	09/20 00	4
Hermine	09/17	09/20	74	999	09/20 00	--
Ivan	09/20	09/27	150	975	09/26 00	1
Jeanne	09/21	10/01	165	970	09/24 12	2
Karl	09/23	09/28	165	970	09/27 06	2
Lisa	10/05	10/09	120	987	10/09 18	1
Mitch	10/22	11/05	287	905	10/26 18	5
Nicole	11/24	12/01	140	979	12/01 00	1

*: UTC Time and Date of maximum intensity means Universal Coordinated Time and differs in +5 hours from Cuba’s Local Time (meridian 75 West of Greenwich)

Individual characteristics of tropical Cyclones in 1998