Hurricane Nadine

Hurricane Nadine was the fourth longest-lived Atlantic hurricane on record. The fourteenth tropical cyclone and named storm of the 2012 Atlantic hurricane season, Nadine developed from a tropical wave located well west of Cape Verde on September 10. By the following day, it strengthened into Tropical Storm Nadine. After initially tracking northwestward, Nadine turned northward while located well east of major landmasses. Early on September 15, Nadine reached hurricane status as it was curving eastward. However, vertical wind shear weakened Nadine back to a tropical storm by September 16. On the following day, the storm began moving northeastward and threatened the Azores; by late on September 19, however, Nadine veered east-southeastward before reaching the islands. Nonetheless, the storm produced tropical storm winds on a few islands. On September 21, the storm curved south-southeastward while located south of the Azores. Later that day, Nadine transitioned into an extratropical low pressure area.

Hurricane Nadine

Category 1 hurricane (SSHWS/NWS)
Nadine at peak intensity on September 30
Formed	September 10, 2012
Dissipated	October 3, 2012
Highest winds	1-minute sustained: 90 mph (150 km/h)
Lowest pressure	978 mbar (hPa); 28.88 inHg
Fatalities	None
Areas affected	Azores
Part of the 2012 Atlantic hurricane season

Due to favorable conditions, the remnants of Nadine regenerated into a tropical cyclone on September 24. After re-developing, the storm executed a cyclonic loop and meandered slowly across the eastern Atlantic. Eventually, Nadine turned south-southwestward, at which time it became nearly stationary. By September 28, the storm curved northwestward and re-strengthened into a hurricane. The tenacious cyclone intensified further and peaked with winds of 90 mph (150 km/h) on September 30. By the following day, however, Nadine weakened back to a 65 mph (100 km/h) tropical storm, as conditions became increasingly unfavorable. Strong wind shear and decreasing sea surface temperatures (SST's) significantly weakened the storm. Nadine transitioned into an extratropical cyclone on October 3, shortly before merged with an approaching cold front northeast of the Azores. The remnants of Nadine passed through the islands on October 4, once again bringing relatively strong winds to the islands.

A large tropical wave emerged into the Atlantic Ocean from the west coast of Africa on September 7.^[1][2] The system passed south of Cape Verde on September 8, with disorganized showers and thunderstorms. Around that time, the National Hurricane Center gave the system a medium chance of tropical cyclogenesis within 48 hours. A low pressure area developed along the axis of the tropical wave on September 9, which caused convective activity to increase further.^[2] The system was assessed with a high chance for tropical cyclone formation on September 10.^[3] Based on Dvorak intensity estimates from the National Oceanic and Atmospheric Administration (NOAA)'s Satellite Analysis Branch (SAB), the National Hurricane Center declared the disturbance as Tropical Depression Fourteen at 1200 UTC on September 10, while located about 885 miles (1,424 km) west of Cape Verde.^[4][2]

Although thunderstorm activity was initially minimal around the center of circulation, the depression had a well-defined convective band.^[4] Late on September 10, convection began to increase slightly near the center, though because Dvorak intensity T-numbers were between 2.0 and 2.5, the depression was not upgraded to a tropical storm.^[5] However, dry air briefly caused showers and thunderstorms to decrease later that day. Initially, it headed just north of due west, but re-curved northwestward on September 11. Later on that day, the depression began to re-gain deep convection. Based on geostationary satellite imagery and scatterometer data, the depression was upgraded to Tropical Storm Nadine at 0000 UTC on September 12.^[2]

Central dense overcast developed and due to favorable conditions, the National Hurricane Center noted the possibility of rapid deepening.^[6] Intensification continued at a quicker on September 12, but not rapid rate; by the end of the day, sustained winds reached 65 mph (105 km/h).^[7][8] By early on September 13, convective banding wrapped almost completely around the center and cloud tops reached temperatures as low as −112 °F (−80 °C). However, because microwave satellite data could not determine if an eye had developed, Nadine was held just below the threshold of hurricane intensity.^[9] The National Hurricane Center noted that "THE WINDOW FOR NADINE TO STRENGTHEN MAY BE CLOSING", citing computer model consensus of an increase in wind shear and little change in structure.^[10] The storm then began experiencing moderate southwesterly wind shear on September 13, generated by a mid- to upper-level trough and a shear axis located a few hundred miles to the west of Nadine. As a result, the storm struggled to developed an eye and the center became more difficult to locate.^[11]

Although it was disorganized, a scatterometer pass indicated tropical storm force winds extended outward up to 230 miles (370 km). From late on September 13 to early on September 14, Nadine began moving west-northwest and eventually north-northeast around the southwestern periphery of the subtropical ridge.^[12] The satellite appearance of Nadine became more ragged by September 14. Despite this, the storm remained just below hurricane status, and the National Hurricane Center noted the possibility of intensification if wind shear were to decrease within the next few days. Nadine turned northward on September 14 as it tracked along the periphery of a subtropical ridge.^[13] Shortly thereafter, a Tropical Rainfall Measuring Mission (TRMM) pass indicated that core convection had began re-organizing. However, because wind shear displaced the mid-level circulation to the north of the low-level circulation, Nadine was not upgraded to a hurricane.^[14]

The National Hurricane Center corrected an earlier prediction and noted that wind shear over Nadine would not decrease within the next five days, but change directions, allowing a slightly more conductive environment for intensification. Because Nadine would approach colder sea surface temperatures (SST's), significant strengthening was considered unlikely.^[14] Due to an increase in satellite intensity estimates and re-organization, Nadine was upgraded to a hurricane at 1800 UTC on September 14. Six hours later, Nadine reached an initial peak intensity with winds of 80 mph (130 km/h).^[2] Satellite imagery indicated that a ragged eye feature was attempting to develop late on September 15.^[15]

Late on September 15, Nadine began "to look a little more ragged" as microwave data observations noted shearing of deep convection to the northeast of the center.^[16] Late on September 16, the tilted eye disappeared, convective bands became more fragmented, and the overall showers and thunderstorms activity waned since early that day.^[17] Nadine weakened back to a tropical storm on September 17.^[2] Around that time, the National Hurricane Center noted that the storm had less convection near the center and had a more asymmetrical appearance. Additionally, a trough in the area caused Nadine to acquire a less tropical satellite appearance on September 17.^[18]

Dry air began impacting Nadine on September 17, though outflow from the storm prevented significant weakening.^[19] Despite a large flare of deep convection over the northern semicircle, Nadine weakened slightly on September 17.^[20] Further weakening occurred on the following day, after the burst in deep convection on September 17 deteriorated. The National Hurricane Center also predicted in an advisory on September 18 that Nadine would transition into an extratropical cyclone by September 21, as the storm could soon encounter colder SST's.^[21] Later on September 18, most of the deep convection dissipated, with the strongest of the remaining showers and thunderstorms activity being located within a band west and northwest of the center.^[22]

Nadine threatened the Azores while moving northeastward and then northward between September 18 and September 19, though a blocking ridge prevented the storm from approaching further toward the islands. Its closest approach to the Azores was about 150 miles (240 km) south-southwest of Flores Island on September 19.^[2] The storm then re-curved east-southeastward on September 20, after the ridge weakened and the mid- to upper-level trough deepened.^[2] By late on September 21, the cloud pattern significant deteriorated, which now composed of only a ragged convective band with warming cloud tops.^[23] Operationally, the National Hurricane Center re-classified Nadine as a subtropical storm at 2100 UTC on September 21, mainly because it had a larger than average and asymmetrical wind field, as well as the development of an upper-level low pressure area near the center.^[24] However, post-season analysis concluded that Nadine transitioned into an extratropical storm three hours prior.^[2]

Early on September 22, the National Hurricane Center noted that regeneration into a tropical cyclone was a distinct possibility.^[25] The remnant low pressure area soon moved over warmer SST's and a low-shear environment, causing deep convection to re-develop. Thus, Nadine regenerated back into a tropical storm at 0000 UTC on September 23. Another blocking ridge over the Azores forced Nadine to move west-northwestward on September 24, causing it to execute a small cyclonic loop. Although winds increased to 60 mph (95 km/h), the storm weakened again and decreased to a 45 mph (75 km/h) tropical storm by on September 25.^[2] Despite this, satellite imagery indicated that Nadine developed an eye-like feature.^[26] However, the National Hurricane Center later noted that it was a cloud-free region near the center of the storm.^[27] By September 26, Nadine curved south-southwestward to southwestward around the southeastern portion of a mid- to upper-level ridge located over the western Atlantic.^[2]

After minimal change in strength for several days, Nadine finally began to intensify on September 27, due to SST's warmer than 79 °F (26 °C). At 1200 UTC on September 28, Nadine re-strengthened into a Category 1 hurricane.^[2] Around the time, satellite imagery indicated that the storm re-developed an eye feature.^[28] After becoming disorganized, the National Hurricane Center erroneously downgraded Nadine to a tropical storm on September 29,^[29] before upgrading it to a hurricane again six hours later.^[30] Nadine had acutally remained a hurricane and was intensifying further.^[2] Winds were increased to 85 mph (140 km/h) on September 30, after the eye became more distinct.^[31] At 1200 UTC, the storm attained its peak intensity with maximum sustained winds of 90 mph (150 km/h) and a minimum barometric pressure of 978 mbar (28.9 inHg).^[2]

After peak intensity, Nadine began weakening once again and deteriorated to a tropical storm at 1200 UTC on October 1.^[2] Northwesterly winds began to increase on October 3, after an upper-level trough that was causing low wind shear moved eastward.^[32] A few hours later, the low-level center became partially exposed,^[33] before becoming fully separated from the convection by 1500 UTC.^[34] Due to strong wind shear and cold sea surface temperatures, showers and thunderstorms rapidly diminished, and by late on October 3, Nadine become devoid of any deep convection.^[35] At 0000 UTC on October 4, Nadine transitioned into an extratropical low pressure area, while located about 195 miles (315 km) southwest of the central Azores. The low moved rapidly northeastward, degenerated into a trough of low pressure, and was absorbed by a cold front later that day.^[2]

Tropical cyclone warnings and watches were issued on two separate occasions as Nadine approached the Azores. At 1000 UTC on September 18, a tropical storm watch was issued for the islands of Flores and Corvo. Although the tropical storm watch was discontinued at 2100 UTC, a tropical storm warning was implemented at that time for the islands of Corvo, Faial, Flores, Graciosa, Pico, São Jorge, and Terceira. At 1500 UTC on September 19, a tropical storm warning was also issued for São Miguel and Santa Maria. All watches and warnings were discontinued by late on September 21. After re-generating, Nadine posed a threat to the Azores again, and thus, a tropical storm watch was issued for the entire archipelago at 1500 UTC on October 1. Nine hours later, 0000 UTC on the following day, the watch was upgraded to a tropical storm warning. After Nadine became extratropical, the warning was discontinued.^[2]

Late on September 20, Flores reported a wind gust of 46 mph (74 km/h).^[36] A sustained wind speed of 62 mph (100 km/h) and a gust up to 81 mph (130 km/h) were reported at Horta on the island of Faial, as Nadine passed to the south on September 21. During the second Azores impact on October 4, the highest sustained wind speed reported was 38 mph (61 km/h) on São Miguel, while the strongest gust was 87 mph (140 km/h) at the Wind Power Plant on Santa Maria.^[2] Nadine lasted a total of 24 days as a tropical, subtropical and post-tropical cyclone, including 22.25 days as a tropical system. This makes it the fourth longest-lasting Atlantic tropical cyclone on record, only behind the 1899 San Ciriaco hurricane at 28 days, Hurricane Ginger in 1971 at 27.25 days and Hurricane Inga in 1969 at 24.75 days. When only counting time spent as a tropical storm or hurricane – 20.75 days – Nadine is the third longest-lasting, behind only Hurricane Ginger in 1971 and the 1899 San Ciriaco hurricane.^[2] When Nadine was upgraded to a hurricane at 1800 UTC on September 14, it marked the third-earliest forming eighth hurricane, behind only an unnamed system in 1893 and Ophelia in 2005.^[37]

• Hurricane Alberto (2000)
• Hurricane Gordon (2006)
• List of longest-lasting Atlantic hurricanes