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Subtropical Storm One (1992)
Encyclopedia
Subtropical Storm One in 1992 was the first recorded Atlantic
subtropical cyclone
during the month of April. It formed on April 21 about 600 miles (1,100 km) southeast of Bermuda
, and tracking northwestward reached subtropical storm status on April 22. The cyclone attained peak winds of 50 mph (85 km/h) before increased wind shear
weakened the storm. It turned to the east, and on April 24 dissipated without affecting land.
separated from the prevailing westerlies
about 600 miles (1,100 km) southeast of Bermuda
. At the time, the system maintained a large comma-shaped cloud pattern, and reports from nearby ships indicated the system was at the surface. Based on its organization and the presence of a low-level circulation, it is estimated the system developed into a subtropical depression
at 1200 UTC on April 21; operationally it was not classified until 27 hours later. Removed from well-defined steering currents, the depression tracked northwestward at 12 mph (19 km/h), and intensified into a subtropical storm early on April 22.
The subtropical storm gradually became better organized with a large convective band in its eastern semicircle, and upon being classified it reached peak winds of 50 mph (85 km/h); a ship reported strong winds near the center of the cyclone, and the National Hurricane Center
remarked the potential for the system transitioning into a tropical cyclone
. With a building ridge
to its southeast, the storm tracked northwestward, and under the influence of an approaching trough
it decelerated as deep convection diminished. On April 23 the cyclone became nearly stationary and weakened to depression status after strong upper-level wind shear
affected the area. A Hurricane Hunters
flight into the system confirmed the decrease in winds; the flight also reported a 1.8° F (1° C) temperature rise in the center, suggesting a warm core and some tropical characteristics.
By early on April 24, the subtropical depression turned eastward, maintaining limited amounts of deep convection on its eastern semicircle. At the time, forecasters anticipated the depression would continue east-northeastward and become an extratropical cyclone
, though the possibility of dissipation was mentioned. By late on April 24, however, the system was too weak to classify using the Dvorak technique
; the National Hurricane Center ceased issuing advisories, and it failed to meet the criteria of a subtropical cyclone. Within 24 hours, the circulation dissipated as the system continued eastward through the westerlies.
. The National Hurricane Center
issued an 18 percent chance the center of the storm would pass within 65 miles (105 km) of the island; however it remained well southeast of the territory. The highest winds reported by a ship was 50 mph (85 km/h), from a vessel with the call signal C6KD7. The ship recorded a pressure of 1004.1 mbar
with swells of 64.4 feet (19.7 m); the decision to issue advisories on the cyclone was based primarily on the ship report.
The storm was the first Atlantic
subtropical cyclone
on record to develop in the month of April. Previously, a tropical or subtropical cyclone had developed in every month but April. In its preliminary report on the cyclone, the National Hurricane Center notes, "subtropical cyclones have only been tracked since 1968 (tropical cyclone records go back to 1871) and it is possible some systems that were designated extratropical prior to 1968 could have been subtropical." Additionally, the subtropical storm was the first not to transition into a tropical cyclone
since 1984
. Subtropical cyclones were not named at the time, and were not named until 2001
; had it been named, it would have been Subtropical Storm Andrew.
Atlantic hurricane
North Atlantic tropical cyclones usually form in the northern hemisphere summer or fall. Tropical cyclones can be categorized by intensity. Tropical storms have one-minute maximum sustained winds of at least 39 mph , while hurricanes have one-minute maximum sustained exceeding 74 mph...
subtropical cyclone
Subtropical cyclone
A subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone. As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical or extratropical cyclones. They were officially recognized by the National...
during the month of April. It formed on April 21 about 600 miles (1,100 km) southeast of Bermuda
Bermuda
Bermuda is a British overseas territory in the North Atlantic Ocean. Located off the east coast of the United States, its nearest landmass is Cape Hatteras, North Carolina, about to the west-northwest. It is about south of Halifax, Nova Scotia, Canada, and northeast of Miami, Florida...
, and tracking northwestward reached subtropical storm status on April 22. The cyclone attained peak winds of 50 mph (85 km/h) before increased 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...
weakened the storm. It turned to the east, and on April 24 dissipated without affecting land.
Meteorological history
On April 21, a low- to mid-level low pressure areaLow pressure area
A low-pressure area, or "low", is a region where the atmospheric pressure at sea level is below that of surrounding locations. Low-pressure systems form under areas of wind divergence which occur in upper levels of the troposphere. The formation process of a low-pressure area is known as...
separated from the prevailing westerlies
Westerlies
The Westerlies, anti-trades, or Prevailing Westerlies, are the prevailing winds in the middle latitudes between 30 and 60 degrees latitude, blowing from the high pressure area in the horse latitudes towards the poles. These prevailing winds blow from the west to the east, and steer extratropical...
about 600 miles (1,100 km) southeast of Bermuda
Bermuda
Bermuda is a British overseas territory in the North Atlantic Ocean. Located off the east coast of the United States, its nearest landmass is Cape Hatteras, North Carolina, about to the west-northwest. It is about south of Halifax, Nova Scotia, Canada, and northeast of Miami, Florida...
. At the time, the system maintained a large comma-shaped cloud pattern, and reports from nearby ships indicated the system was at the surface. Based on its organization and the presence of a low-level circulation, it is estimated the system developed into a subtropical depression
Subtropical cyclone
A subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone. As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical or extratropical cyclones. They were officially recognized by the National...
at 1200 UTC on April 21; operationally it was not classified until 27 hours later. Removed from well-defined steering currents, the depression tracked northwestward at 12 mph (19 km/h), and intensified into a subtropical storm early on April 22.
The subtropical storm gradually became better organized with a large convective band in its eastern semicircle, and upon being classified it reached peak winds of 50 mph (85 km/h); a ship reported strong winds near the center of the cyclone, and the National Hurricane Center
National Hurricane Center
The National Hurricane Center , located at Florida International University in Miami, Florida, is the division of the National Weather Service responsible for tracking and predicting weather systems within the tropics between the Prime Meridian and the 140th meridian west poleward to the 30th...
remarked the potential for the system transitioning into a tropical cyclone
Tropical cyclone
A 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...
. With a building ridge
Ridge (meteorology)
A ridge is an elongated region of relatively high atmospheric pressure, the opposite of a trough....
to its southeast, the storm tracked northwestward, and under the influence of an approaching 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...
it decelerated as deep convection diminished. On April 23 the cyclone became nearly stationary and weakened to depression status after strong upper-level 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...
affected the area. A Hurricane Hunters
Hurricane Hunters
The Hurricane Hunters are aircraft that fly into tropical cyclones in the North Atlantic Ocean and Northeastern Pacific Ocean for the specific purpose of directly measuring weather data in and around those storms. In the United States, the Air Force, Navy, and NOAA units have all participated in...
flight into the system confirmed the decrease in winds; the flight also reported a 1.8° F (1° C) temperature rise in the center, suggesting a warm core and some tropical characteristics.
By early on April 24, the subtropical depression turned eastward, maintaining limited amounts of deep convection on its eastern semicircle. At the time, forecasters anticipated the depression would continue east-northeastward and become 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...
, though the possibility of dissipation was mentioned. By late on April 24, however, the system was too weak to classify using the Dvorak technique
Dvorak technique
The Dvorak technique is a widely used system to subjectively estimate tropical cyclone intensity based solely on visible and infrared satellite images. Several agencies issue Dvorak intensity numbers for cyclones of sufficient intensity...
; the National Hurricane Center ceased issuing advisories, and it failed to meet the criteria of a subtropical cyclone. Within 24 hours, the circulation dissipated as the system continued eastward through the westerlies.
Impact, records, and naming
Initially, the subtropical storm appeared to be a threat to BermudaBermuda
Bermuda is a British overseas territory in the North Atlantic Ocean. Located off the east coast of the United States, its nearest landmass is Cape Hatteras, North Carolina, about to the west-northwest. It is about south of Halifax, Nova Scotia, Canada, and northeast of Miami, Florida...
. The National Hurricane Center
National Hurricane Center
The National Hurricane Center , located at Florida International University in Miami, Florida, is the division of the National Weather Service responsible for tracking and predicting weather systems within the tropics between the Prime Meridian and the 140th meridian west poleward to the 30th...
issued an 18 percent chance the center of the storm would pass within 65 miles (105 km) of the island; however it remained well southeast of the territory. The highest winds reported by a ship was 50 mph (85 km/h), from a vessel with the call signal C6KD7. The ship recorded a pressure of 1004.1 mbar
Bar (unit)
The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...
with swells of 64.4 feet (19.7 m); the decision to issue advisories on the cyclone was based primarily on the ship report.
The storm was the first Atlantic
Atlantic hurricane
North Atlantic tropical cyclones usually form in the northern hemisphere summer or fall. Tropical cyclones can be categorized by intensity. Tropical storms have one-minute maximum sustained winds of at least 39 mph , while hurricanes have one-minute maximum sustained exceeding 74 mph...
subtropical cyclone
Subtropical cyclone
A subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone. As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical or extratropical cyclones. They were officially recognized by the National...
on record to develop in the month of April. Previously, a tropical or subtropical cyclone had developed in every month but April. In its preliminary report on the cyclone, the National Hurricane Center notes, "subtropical cyclones have only been tracked since 1968 (tropical cyclone records go back to 1871) and it is possible some systems that were designated extratropical prior to 1968 could have been subtropical." Additionally, the subtropical storm was the first not to transition into a tropical cyclone
Tropical cyclone
A 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...
since 1984
1984 Atlantic hurricane season
The 1984 Atlantic hurricane season officially began on June 1, 1984, and lasted until November 30, 1984. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. The 1984 season was an active one in terms of named storms, but most of them...
. Subtropical cyclones were not named at the time, and were not named until 2001
2001 Atlantic hurricane season
The 2001 Atlantic hurricane season was a fairly active Atlantic hurricane season that produced 17 tropical cyclones, 15 named storms, nine hurricanes, and four major hurricanes. The season officially lasted from June 1, 2001, to November 30, 2001, dates which by convention limit the period of each...
; had it been named, it would have been Subtropical Storm Andrew.
See also
- Subtropical cycloneSubtropical cycloneA subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone. As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical or extratropical cyclones. They were officially recognized by the National...
- Timeline of the 1992 Atlantic hurricane seasonTimeline of the 1992 Atlantic hurricane seasonThe 1992 Atlantic hurricane season was a below-average season that produced six named tropical cyclones. The season officially started on June 1, 1992 and finished on November 30; however, Subtropical Storm One formed outside the official timeline on April 21...
