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Hurricane Lisa (1998)
Encyclopedia
Hurricane Lisa was the 12th known tropical cyclone of the 1998 Atlantic hurricane season
. The storm developed from a tropical wave
that entered the Atlantic Ocean on September 29 from the coast of Africa. By October 4, a low-level circulation developed, and the system was declared a tropical depression early on October 5; it was upgraded to a tropical storm that same day. Initially moving towards the northwest, Lisa turned to the northeast, and subsequently accelerated towards the north, attaining hurricane status before transitioning into an extratropical cyclone
over the cold waters of the north Atlantic. As Lisa remained far from land, no damage was reported.
emerged from the east coast of Africa and entered the Atlantic Ocean, with fairly well-organized associated cloud activity. However, by the next day the wave became intermingled within the Intertropical Convergence Zone
that was active throughout the tropical Atlantic. By October 3, the system became more distinguishable and better defined, as convective activity
began to increase. Signs of a low-level circulation arose on October 4, while the system was located roughly midway between Africa and the Lesser Antilles
. It is estimated that the system became a tropical depression at 0000 UTC on October 5. The same wave eventually crossed into the eastern Pacific Ocean
and spawned Hurricane Lester
.
Initially, the depression was disorganized as a result of strong wind shear
that was generated by an upper-level low pressure system to the northwest of the storm. The western half of the depression's circulation was exposed, though the eastern semicircle maintained deep convection. On October 5, the storm was upgraded to Tropical Storm Lisa; operational reports suggest that it had been a tropical storm for the past 18 hours. The same low that produced the wind shear also caused a weakness in the ridge to the north, causing the storm to begin a turn towards the north. At the time, further intensification was deemed unlikely due to the shear. However, Lisa consisted of a fairly large circulation that was more resilient to the shear than tropical cyclones with smaller circulations. During the morning of October 7, the center of circulation was intermittently located beneath the deep convection. A nearby buoy reported winds of near 70 miles per hour (112.7 km/h), indicating that the storm had attained winds of about 60 mph (96.6 km/h). A strong baroclinic trough
evolved into a deep low pressure system in the central North Atlantic, which caused Lisa to turn towards the northeast.
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Early on October 8, the storm became better-defined on satellite imagery. Later that day, thunderstorm activity persisted near the center, and banding features developed, indications of intensification. The strengthening was attributed to weaker wind shear, or interaction with the trough. In addition, an eye
was "trying to form". Lisa accelerated towards the northeast, with forward speed reaching over 58 miles per hour (93.3 km/h) during the afternoon of October 9. That same day, the storm turned towards the north in response to the deep low to the west, and a strong high pressure system to the east. At 1200 UTC, the cyclone attained Category 1 hurricane status on the Saffir-Simpson Hurricane Scale
. Shortly thereafter, while over the cold waters of the north Atlantic, Lisa began to lose tropical characteristics, transitioning into an extratropical cyclone
. It merged with an extratropical frontal system
, and by October 10 a well-defined circulation was no longer identifiable.
were issued.
1998 Atlantic hurricane season
The 1998 Atlantic hurricane season officially began on June 1, 1998, and lasted until November 30, 1998. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin; however, the season extended through December 1 as Hurricane Nicole remained...
. The storm developed from a tropical wave
Tropical wave
Tropical waves, easterly waves, or tropical easterly waves, also known as African easterly waves in the Atlantic region, are a type of atmospheric trough, an elongated area of relatively low air pressure, oriented north to south, which move from east to west across the tropics causing areas of...
that entered the Atlantic Ocean on September 29 from the coast of Africa. By October 4, a low-level circulation developed, and the system was declared a tropical depression early on October 5; it was upgraded to a tropical storm that same day. Initially moving towards the northwest, Lisa turned to the northeast, and subsequently accelerated towards the north, attaining hurricane status before transitioning into an extratropical cyclone
Extratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...
over the cold waters of the north Atlantic. As Lisa remained far from land, no damage was reported.
Meteorological history
On September 29, 1998, a tropical waveTropical wave
Tropical waves, easterly waves, or tropical easterly waves, also known as African easterly waves in the Atlantic region, are a type of atmospheric trough, an elongated area of relatively low air pressure, oriented north to south, which move from east to west across the tropics causing areas of...
emerged from the east coast of Africa and entered the Atlantic Ocean, with fairly well-organized associated cloud activity. However, by the next day the wave became intermingled within the Intertropical Convergence Zone
Intertropical Convergence Zone
The Intertropical Convergence Zone , known by sailors as The Doldrums, is the area encircling the earth near the equator where winds originating in the northern and southern hemispheres come together....
that was active throughout the tropical Atlantic. By October 3, the system became more distinguishable and better defined, as convective activity
Atmospheric convection
Atmospheric convection is the result of a parcel-environment instability, or temperature difference, layer in the atmosphere. Different lapse rates within dry and moist air lead to instability. Mixing of air during the day which expands the height of the planetary boundary layer leads to...
began to increase. Signs of a low-level circulation arose on October 4, while the system was located roughly midway between Africa and the Lesser Antilles
Lesser Antilles
The Lesser Antilles are a long, partly volcanic island arc in the Western Hemisphere. Most of its islands form the eastern boundary of the Caribbean Sea with the Atlantic Ocean, with the remainder located in the southern Caribbean just north of South America...
. It is estimated that the system became a tropical depression at 0000 UTC on October 5. The same wave eventually crossed into the eastern Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
and spawned Hurricane Lester
Hurricane Lester (1998)
Hurricane Lester was the fifteenth tropical cyclone, twelfth named storm and eighth hurricane of the 1998 Pacific hurricane season. Lester originated from a tropical wave that emerged off the coast of Africa on September 29. Under favorable conditions, the storm was classified as a tropical...
.
Initially, the depression was disorganized as a result of strong wind shear
Wind shear
Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...
that was generated by an upper-level low pressure system to the northwest of the storm. The western half of the depression's circulation was exposed, though the eastern semicircle maintained deep convection. On October 5, the storm was upgraded to Tropical Storm Lisa; operational reports suggest that it had been a tropical storm for the past 18 hours. The same low that produced the wind shear also caused a weakness in the ridge to the north, causing the storm to begin a turn towards the north. At the time, further intensification was deemed unlikely due to the shear. However, Lisa consisted of a fairly large circulation that was more resilient to the shear than tropical cyclones with smaller circulations. During the morning of October 7, the center of circulation was intermittently located beneath the deep convection. A nearby buoy reported winds of near 70 miles per hour (112.7 km/h), indicating that the storm had attained winds of about 60 mph (96.6 km/h). A strong baroclinic trough
Trough (meteorology)
A trough is an elongated region of relatively low atmospheric pressure, often associated with fronts.Unlike fronts, there is not a universal symbol for a trough on a weather chart. The weather charts in some countries or regions mark troughs by a line. In the United States, a trough may be marked...
evolved into a deep low pressure system in the central North Atlantic, which caused Lisa to turn towards the northeast.
Eye (cyclone)
The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the second most severe weather of a cyclone...
was "trying to form". Lisa accelerated towards the northeast, with forward speed reaching over 58 miles per hour (93.3 km/h) during the afternoon of October 9. That same day, the storm turned towards the north in response to the deep low to the west, and a strong high pressure system to the east. At 1200 UTC, the cyclone attained Category 1 hurricane status on the Saffir-Simpson Hurricane Scale
Saffir-Simpson Hurricane Scale
The Saffir–Simpson Hurricane Scale , or the Saffir–Simpson Hurricane Wind Scale , classifies hurricanes — Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms — into five categories distinguished by the intensities of their sustained winds...
. Shortly thereafter, while over the cold waters of the north Atlantic, Lisa began to lose tropical characteristics, transitioning into an extratropical cyclone
Extratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...
. It merged with an extratropical frontal system
Weather front
A weather front is a boundary separating two masses of air of different densities, and is the principal cause of meteorological phenomena. In surface weather analyses, fronts are depicted using various colored lines and symbols, depending on the type of front...
, and by October 10 a well-defined circulation was no longer identifiable.
Impact and naming
Since Lisa remained away from land, no effects, property damage or fatalities were reported; no ships were affected, and no tropical cyclone warnings and watchesTropical cyclone warnings and watches
Warnings and watches are two levels of alert issued by national weather forecasting bodies to coastal areas threatened by the imminent approach of a tropical cyclone of tropical storm or hurricane intensity. They are notices to the local population and civil authorities to make appropriate...
were issued.
See also
- List of Atlantic hurricanes
- 1998 Atlantic hurricane season1998 Atlantic hurricane seasonThe 1998 Atlantic hurricane season officially began on June 1, 1998, and lasted until November 30, 1998. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin; however, the season extended through December 1 as Hurricane Nicole remained...
- Tropical cycloneTropical cycloneA tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...
- Extratropical cycloneExtratropical cycloneExtratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...