The 2005 Azores subtropical storm was the 19th nameable storm and only

subtropical storm A subtropical cyclone is a weather system that has some characteristics of both tropical and an extratropical cyclone. As early as the 1950s, meteorologists were uncertain whether they should be characterized as tropical or extratropical cyclo ...

of the extremely active

2005 Atlantic hurricane season The 2005 Atlantic hurricane season was the most active Atlantic hurricane season in history, until the record was broken 15 years later in 2020. The season broke numerous records at the time, with 28 tropical or subtropical storms recorded. ...

. It was not officially named by the US

National Hurricane Center The National Hurricane Center (NHC) is the division of the United States' NOAA/National Weather Service responsible for tracking and predicting tropical weather systems between the Prime Meridian and the 140th meridian west poleward to the 3 ...

as it was operationally classified as a non-tropical low. The storm developed in the eastern Atlantic Ocean out of a low-pressure area that gained subtropical characteristics on 4 October. The storm was short-lived, crossing over the

Azores ) , motto =( en, "Rather die free than subjected in peace") , anthem= ( en, "Anthem of the Azores") , image_map=Locator_map_of_Azores_in_EU.svg , map_alt=Location of the Azores within the European Union , map_caption=Location of the Azores wi ...

later on 4 October before becoming

extratropical Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of p ...

again on 5 October. No damages or fatalities were reported during that time. After being absorbed into a

cold front A cold front is the leading edge of a cooler mass of air at ground level that replaces a warmer mass of air and lies within a pronounced surface trough of low pressure. It often forms behind an extratropical cyclone (to the west in the Northern ...

, the system went on to become

Hurricane Vince Hurricane Vince was an unusual hurricane that developed in the northeastern Atlantic basin. Forming in October during the 2005 Atlantic hurricane season, it strengthened over waters thought to be too cold for tropical development. Vince was the ...

, which affected the

Iberian Peninsula The Iberian Peninsula (), ** * Aragonese and Occitan: ''Peninsula Iberica'' ** ** * french: Péninsule Ibérique * mwl, Península Eibérica * eu, Iberiar penintsula also known as Iberia, is a peninsula in southwestern Europe, def ...

. Months after the hurricane season, when the National Hurricane Center was performing its annual review of the season and its named storms, forecasters Jack Beven and Eric Blake identified this previously unnoticed subtropical storm. Despite its unusual location and wide wind field, the system had a well-defined centre convecting around a warm core.

Meteorological history

The system originated out of an upper-level low just west of the

Canary Islands The Canary Islands (; es, :es:Canarias, Canarias, ), also known informally as the Canaries, are a Spanish Autonomous communities of Spain, autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to ...

on 28 September. The low organized itself over the next days, producing several bursts of convection. While remaining non-tropical with a

cold core A cold-core low, also known as an upper level low or cold-core cyclone, is a cyclone aloft which has an associated cold pool of air residing at high altitude within the Earth's troposphere, without a frontal structure. It is a low pressure syste ...

it moved gradually west to northwest. On 3 October, it became a broad surface low about 400 nautical miles (740 km, 460 mi) southwest of

São Miguel Island São Miguel Island (; Portuguese for "Saint Michael"), nicknamed "The Green Island" (''Ilha Verde''), is the largest and most populous island in the Portuguese archipelago of the Azores. The island covers and has around 140,000 inhabitants, wi ...

in the

. Early on 4 October, convection increased as the surface low organized itself, and the system became a subtropical depression. Around the same time, the depression turned northeast into a

warm sector A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient. Warm fronts lie within broader troughs of low pressure than cold fro ...

ahead of an oncoming cold front and strengthened into a

. The system continued to track northeast and strengthened slightly, reaching its peak intensity of 85 km/h (50 mph) as it approached the Azores that evening. After tracking through the area, the storm weakened slightly as it moved to the north-northeast. Through an interaction with the cold front early on 5 October, the subtropical storm became extratropical. The system was fully absorbed by the front later that day. The newly absorbed system would separate from the dissolving frontal system and become Subtropical Storm Vince on 8 October. At the time, the system was not believed to have been subtropical. However, there were several post-

season A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's tilted orbit around the Sun. In temperate and ...

findings that confirmed that the system was indeed one. The first finding was the cloud pattern, which had deep

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the c ...

around the centre and was better organized with a well-defined centre of circulation. In addition, the system had a warm core more typical of tropical cyclones as opposed to the cold core of extratropical cyclones. The warm-core nature also meant that there were no warm or

s attached to the system, as temperatures did not change ahead of and behind the system, until an unrelated cold front passed the Azores. Satellite imagery suggested that the system was briefly a tropical storm as the warm core was found; however, the widespread wind field and the presence of an upper-level trough confirmed that it was only subtropical.

Impact, classification and records

Tropical storm-force winds were reported across parts of the Azores, primarily on the eastern islands. The strongest winds were reported on

Santa Maria Island Santa Maria () is an island in the eastern group of the Azores archipelago (south of the island of São Miguel) and the southernmost island in the Azores. The island is known for its white sand beaches, distinctive chimneys, and dry warm weath ...

, where 10-minute sustained winds reached 79 km/h (49 mph) with gusts to 94 km/h (59 mph).

Ponta Delgada Ponta Delgada (; ) is the largest municipality ('' concelho'') and economic capital of the Autonomous Region of the Azores in Portugal. It is located on São Miguel Island, the largest and most populous in the archipelago. As of 2021, it has 67, ...

faced 61 km/h (38 mph) winds, with the peak recorded gust being 85 km/h (52 mph). No damage or fatalities were reported. The 2005 Azores storm was not classified as a subtropical storm until April 2006, after a reassessment by the National Hurricane Center. Had it been operationally classified as such, it would have been named ''Tammy''. Every year, the

(NHC) re-analyzes the systems of the past hurricane season and revises the storm history if there is new data that was operationally unavailable. This reanalysis revealed that the storm became a subtropical storm on 4 October, making it the earliest forming 19th Atlantic tropical or subtropical storm on record. The previous record holder was an unnamed 1933 tropical storm that developed on 26 October. It held this distinction until 2020, when

Hurricane Teddy Hurricane Teddy was a large and powerful Cape Verde hurricane that was the fifth-largest Atlantic hurricane by diameter of gale-force winds recorded. Teddy produced large swells along the coast of the Eastern United States and Atlantic Canada in ...

attained tropical storm strength on 14 September.

References

External links

* NHC's on the storm {{DEFAULTSORT:2005 Azores Subtropical Storm Azores Subtropical Storm, 2005 Hurricanes in the Azores Subtropical storms Azores ST

Meteorological history

Impact, classification and records

See also

References

External links