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The 2005 Azores subtropical storm was the 19th nameable storm and only subtropical storm of the extremely active
2005 Atlantic hurricane season The 2005 Atlantic hurricane season was a record-breaking, devastating and deadly Atlantic hurricane season. It is the second-costliest hurricane season, just behind the 2017 season And 2024. It featured 28 tropical and subtropical storms, ...
. It was not named by the
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 IERS Reference Meridian, Prime Meridian and the 140th meridian ...
as it was operationally classified as an extratropical low. It developed in the eastern Atlantic Ocean, an unusual region for late-season tropical cyclogenesis. Nonetheless, the system was able to generate a well-defined centre convecting around a warm core on 4 October. The system was short-lived, crossing over the
Azores The Azores ( , , ; , ), officially the Autonomous Region of the Azores (), is one of the two autonomous regions of Portugal (along with Madeira). It is an archipelago composed of nine volcanic islands in the Macaronesia region of the North Atl ...
later on 4 October before becoming extratropical again on 5 October. No damages or fatalities were reported during that time. Its remnants were soon 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 (meteorology), trough of Low-pressure area, low pressure. It often forms behind an extratropica ...
. That system went on to become Hurricane Vince, which affected the
Iberian Peninsula The Iberian Peninsula ( ), also known as Iberia, is a peninsula in south-western Europe. Mostly separated from the rest of the European landmass by the Pyrenees, it includes the territories of peninsular Spain and Continental Portugal, comprisin ...
. The subtropical nature of this unnamed system was determined several months after the fact, while the National Hurricane Center was performing its annual review of the season. Upon reclassification, the storm was entered into
HURDAT The Hurricane Databases (HURDAT), managed by the National Hurricane Center (NHC), are two separate databases that contain details on tropical cyclones that have occurred within the Atlantic Ocean and Eastern Pacific Ocean since 1851 and 1949 resp ...
, the official hurricane database.


Meteorological history

The system originated out of an upper-level low just west of the
Canary Islands The Canary Islands (; ) or Canaries are an archipelago in the Atlantic Ocean and the southernmost Autonomous communities of Spain, Autonomous Community of Spain. They are located in the northwest of Africa, with the closest point to the cont ...
on 28 September. The low organized itself over the next days, producing several bursts of convection. While remaining non-tropical with a cold core it moved gradually west to northwest. On 3 October, it became a broad surface low about southwest of
São Miguel Island São Miguel Island (; ), nicknamed "The Green Island" (), is the largest and most populous island in the Portugal, Portuguese archipelago of the Azores. The island covers and has around 140,000 inhabitants, with 45,000 people residing in Ponta D ...
in the
Azores The Azores ( , , ; , ), officially the Autonomous Region of the Azores (), is one of the two autonomous regions of Portugal (along with Madeira). It is an archipelago composed of nine volcanic islands in the Macaronesia region of the North Atl ...
. 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 ahead of an oncoming cold front and strengthened into a subtropical storm. The system continued to track northeast and strengthened slightly, reaching its peak intensity of 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 axial tilt, tilted orbit around the Sun. In temperat ...
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 flow, multiphase fluid flow that occurs Spontaneous process, spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoy ...
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
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 (meteorology), trough of Low-pressure area, low pressure. It often forms behind an extratropica ...
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, where 10-minute sustained winds reached with gusts to .
Ponta Delgada Ponta Delgada (; ) is the largest municipality (''concelho'') and executive 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 67,2 ...
faced winds, with the peak recorded gust being . 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
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 IERS Reference Meridian, Prime Meridian and the 140th meridian ...
(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 attained tropical storm strength on 14 September.


See also

* Timeline of the 2005 Atlantic hurricane season * List of Azores hurricanes * List of unnamed tropical cyclones


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