Meteorological history of Hurricane Dorian

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Hurricane Dorian
Category 5 major hurricane (SSHWS/NWS)
File:Dorian 2019 track.png
Map plotting the track and intensity of Hurricane Dorian according to the Saffir–Simpson scale
Formed August 24, 2019 (2019-08-24)
Dissipated Currently active
Highest winds 1-minute sustained: 185 mph (295 km/h)
Lowest pressure 910 mbar (hPa); 26.87 inHg
Areas affected Lesser Antilles, Puerto Rico, the Bahamas (particularly the Abaco Islands and Grand Bahama), Southeastern United States
Part of the 2019 Atlantic hurricane season
Template:Hurricane Dorian related

Hurricane Dorian was the strongest hurricane to affect the northwestern Bahamas on record, causing catastrophic damage in the Abaco Islands and Grand Bahama in early September 2019. The fifth tropical cyclone, fourth named storm, second hurricane, and first major hurricane of the annual hurricane season, Dorian originated from a westward traveling tropical wave that was located over a thousand miles east of the Windward Islands on August 23. The disturbance rapidly organized and became a tropical depression and later a tropical storm, both on August 24. The newly formed Dorian struggled to intensify over the next few days due to a combination of dry air and vertical wind shear. The storm passed over Barbados and entered the Carribean Sea on August 26 as it gradually strengthened. Dorian made landfall in St. Lucia on the next day, which caused serious disruption to the system's structure. Initially predicted to strike Hispaniola, Dorian's track gradually shifted to the east as the storm neared Greater Antilles. Due to land interaction and the dry air, Dorian's center reformed north of its previous location, causing the system's track to shift northward. The storm then turned towards the northwest as it traveled through a weakness in a ridge. A combination of the dry air and shear relaxing as well as the warm sea surface temperatures, allowed Dorian to become a Category 1 hurricane as it passed over St. Thomas on August 28. The storm developed an eye in satellite imagery soon after, but dry air still continued to disrupt the system. The commencement of an eyewall replacement cycle on August 29 temporarily impeded intensification, but Dorian completed the cycle the next morning and soon resumed strengthening.

A spurt of rapid deepening led Dorian to achieve Category 4 status on the Saffir–Simpson scale early on August 31, with a distinct, sharply-defined eye developing within a symmetric central dense overcast. During this time, the intensifying hurricane turned west-northwestward then westward as a ridge built in the subtropics to the north. Another period of rapid strengthening on September 1 saw Dorian achieve Category 5 intensity – the highest classification on the Saffir–Simpson scale – at 12:00 UTC. Dorian's cloud tops continued to cool and the eye increased further in definition as the hurricane approached the Bahamas, with the winds reaching 185 mph (295 km/h) just five hours later as Dorian made landfall in Elbow Cay and then Marsh Harbour of the Abaco Islands. The central pressure reached a low of 910 mbar (hPa; 26.87 inHg) at 19:00 UTC September 1 while the eye was still over Great Abaco, representing Dorian's peak intensity. Steady weakening took place thereafter as Dorian moved over Grand Bahama and slowed to a standstill due to the collapse of the aforementioned steering ridge; however, Dorian remained a major hurricane until it began to move away from the Bahamas late on September 3.

Origins and track through the Lesser Antilles

File:Dorian 2019-08-25 1715Z.jpg
Tropical Storm Dorian gradually strengthening to the east of the Lesser Antilles on August 25.

The origins of Dorian can be traced back to a tropical wave that was located approximately 1,400 mi (2,255 km) east-southeast of the Windward Islands on August 23, 2019. The National Hurricane Center (NHC) initially predicted slow development as the wave progressed westward at 15 mph (24 km/h),[1] however, it rapidly organized over the next day, spawning Tropical Depression Five at 15:00 UTC on August 24. At that time, the system's southeastern outflow was restricted due to moderate easterly vertical wind shear.[2] Six hours later, the depression was upgraded to Tropical Storm Dorian after having developed banding features and a 10 mi (15 km) wide eye-like feature.[3] Despite being located in an environment of warm sea surface temperatures, Dorian only gradually strengthened over the next few days as a result of the shear as well as abundant mid-level dry air. Early in its existence, the tropical storm mainly produced short lived bursts of convection near its center,[4] however, Dorian's convective and internal structures became more organized as the wind shear relaxed on August 25.[5][6] Continuing westward under the influence of a subtropical ridge to its north, Dorian's intensification was hindered by dry air ingestion.[7] Dorian reached an initial peak of 60 mph (95 km/h) around 09:00 UTC on August 26,[8] before a United States Air Force Hurricane Hunter aircraft discovered that the system was not as strong as previous estimates had indicated early on the next day.[9] A few hours later, Dorian passed over Barbados, entering the Carribean Sea. At that time, composite radar showed the system lacked a strong inner core.[10] The tropical storm made a landfall in St. Lucia around 10:00 UTC on August 27, resulting in severe disruption of the small system's center and mid-level circulation.[11] Soon after, Dorian's center re-developed farther north and convection fluctuated as the storm continued to be battered by dry air and interacted with the Leeward and Windward islands. Dorian briefly developed a 10 mi (15 km) wide eye on radar on a couple occasions, but it quickly eroded due to the storm's instability. Despite the dry air, the system's upper-level outflow had expanded and become more symmetrical.[12]

File:Dorian 2019-08-28 1520Z.jpg
Tropical Storm Dorian passing by Puerto Rico and over the Virgin Islands on August 28.

Although Dorian was initially forecast to make landfall in Hispaniola and subsequently weaken or dissipate over the island, the system's track shifted considerably eastward by August 28.[13][5] After the aforementioned center reformation, the track was shifted due to Dorian's more northward position. The new forecast predicted landfall in Puerto Rico as well as a stronger Dorian,[12] however, as the storm took on a more northwesterly direction as a result of a weakness in the ridge caused by a mid- to upper-level low located to the north of Hispaniola, the track shifted to the eastern edge of Puerto Rico.[13] Dorian began strengthening again around 09:00 UTC on August 28, as it banding features became more prominent and a partial eyewall was discovered.[14] The storm continued to strengthen, becoming a Category 1 hurricane around 18:00 UTC on that day as it passed directly over St. Thomas, east of Puerto Rico.[15] The cloud pattern of Dorian continued to organize, with an eye becoming apparent on satellite imagery.[16] The NHC forecasted additional strengthening as the storm would remain in a favorable environment with an increasingly moist mid-level, sea temperatures near or over 84 °F (29 °C), and low wind shear. Even though the storm had strengthened and developed a more defined eye,[17] some dry air penetrated the eyewall early on August 29, the result of which was a cloud- and rain-filled eye and slightly higher surface pressure. Around that time, wind shear temporarily increased to 10–15 mph (16–24 km/h)[18], before relaxing once again. Later in the day, a NOAA Hurricane Hunter aircraft indicated that concentric eyewalls were present, indicating that an eyewall replacement cycle had commenced. Despite this, the aircraft discovered that the central pressure had fallen, but did not find any stronger winds as Dorian continued to track towards the northwest.[19]

Rapid intensification and peak intensity

By the morning of August 30, Dorian completed the eyewall replacement cycle and resumed its intensification trend, with reconnaissance aircraft reporting that Dorian's winds increased to 105 mph (165 km/h) at 03:00 UTC, making Dorian a Category 2 hurricane. The pressure, meanwhile, fell to 977 mbar (hPa; 28.85 inHg) as Dorian's central dense overcast grew in size.[20] Immediately afterwards, the intensification trend slowed once again as the upper-level low steering the system to the northwest generated some southwesterly shear over the hurricane.[21] Through the rest of August 30, however, the upper-level low began to retreat to the west, reducing the wind shear and allowing Dorian to reorganize.[22] Consequently, Dorian reached major hurricane intensity at 18:00 UTC.[23] In the evening, the eye of Dorian cleared out and became surrounded by a ring of deep convection. Meanwhile, a burst of lightning activity occurred in the northwest eyewall, heralding further intensification.[24][25] At 00:30 UTC on August 31, Hurricane Hunter aircraft revealed that Dorian had rapidly reached Category 4 status, with surface winds measured to be near 130 mph (215 km/h).[26] The aircraft also reported that by 03:00 UTC, the pressure had fallen by 22 mbar (hPa; 0.65 inHg) in the past 24 hours. With Dorian passing over sea surface temperatures of 29 °C (84 °F), the NHC noted strengthening was unlikely to have ended.[27] Indeed, the satellite presentation of Dorian continued to improve, with the eye increasing in definition and stabilizing at a diameter of about 15 nmi (28 km; 17 mi). The winds rose to 150 mph (240 km/h) at 15:00 UTC August 31,[28] by which time Dorian was centered just 260 mi (415 km) east-northeast of the northwestern Bahamas.[29]

File:Dorian 2019-09-01 1840Z.jpg
Dorian approaching peak intensity over the Abacos on September 1.

While Dorian intensified, a ridge began to build over the subtropics north of the hurricane, causing Dorian to track more westward straight towards the Abaco Islands.[30] For the rest of August 31 and the morning of September 1, Dorian continued to maintain its intensity, with the NHC noting that Dorian's cloud pattern "remain[ed] very impressive".[31] Afterwards, Dorian began another period of rapid intensification, reaching Category 5 status at 12:00 UTC just 35 mi (55 km) east of Great Abaco Island.[32] The eye of Dorian began to demonstrate a very pronounced stadium effect—a condition where the clouds of a hurricane's eyewall curve outward from the surface with height, such that the top of the eye resembles an open dome. Just three hours later at 15:00 UTC, a Hurricane Hunter aircraft in Dorian's eyewall measured flight-level winds of 183 mph (295 km/h) and its stepped frequency microwave radiometer recorded winds of up to 196 mph (315 km/h), while a dropsonde released by the aircraft recorded a surface wind gust of 203 mph (326 km/h). At this time, the NHC estimated the one-minute sustained winds to have reached 180 mph (285 km/h), making Dorian the strongest hurricane to impact the northwestern Bahamas on record.[33] Further deepening occurred as Dorian began to make landfall over the Abaco Islands, with one-minute sustained winds reaching 185 mph (295 km/h) and the pressure dropping to 911 mbar (hPa; 26.90 inHg) over the next one and a half hours; this was the intensity at which Dorian made landfall in Elbow Cay at 16:40 UTC September 1.[34] A subsequent landfall at Marsh Harbour occurred at 18:00 UTC at the same intensity.[35][36] Dorian ultimately reached its peak intensity over land as the pressure continued to fall further to 910 mbar (hPa; 26.87 inHg) at 19:00 UTC.[37]

Stalling over the Bahamas

File:Dorian 2019-09-02 1520Z by ISS-60.jpg
Dorian over Grand Bahama on September 2 as viewed from the International Space Station.

Shortly after peak intensity, Dorian began to undergo another eyewall replacement cycle, with concentric eyewalls observed on a Hurricane Hunter mission into the system at around 03:00 UTC September 2. However, Dorian remained a potent Category 5 hurricane with winds of 180 mph (285 km/h) as it made a third Bahamas landfall over Grand Bahama around that time.[38] Simultaneously, the ridge north of Dorian began to weaken due to the approach of a mid- to upper-level trough moving across the Eastern United States, resulting in a weaker westward steering flow. Consequently, Dorian began to slow down while over Grand Bahama, coming to a near standstill by 09:00 UTC with the center remaining over land. Despite the eyewall cycle, the hurricane retained a distinct 20 nmi (23 mi; 37 km) eye encircled by very cold cloud tops.[39] Upwelling of cooler waters beneath Dorian, however, facilitated further weakening, with Dorian falling to Category 4 intensity at 15:00 UTC September 2.[40]

Over the next 18 hours, Dorian remained almost stationary over Grand Bahama as steering currents remained weak, while weakening further to Category 3 status at 05:00 UTC September 3 with the eye becoming less defined on radar and infrared imagery.[41][42] With a displacement of just 25 mi (40 km) over the course of a day, Dorian became one of the slowest-moving hurricanes on record.[43] Throughout the entire period of time that Dorian spent over Grand Bahama, it remained a major hurricane. Parts of Grand Bahama experienced the eyewall for more than 25 hours, including five hours while Dorian was at Category 5 intensity; meanwhile Halls Point spent over 11 hours within Dorian's eye.[44] During this period, Dorian brought an estimated 3.0 ft (0.91 m) of rain to the Bahamas, along with a storm surge of over 18 ft (5.5 m).[45][46]

Northwestward turn and dissipation

Dorian began a northwestward motion around 15:00 UTC on September 3 after having stalled over the Bahamas. At the same time, the eye had become cloud-filled, larger, and more ragged. Data collected by reconnaissance aircraft and buoys indicated that the wind field of the storm was expanding.[47] While Dorian slowly weakened over the next day, the eye's distinctness waxed and waned as the system continued to pick up forward speed.[48][49] Soon after, clouds in the eyewall began to cool as Dorian began to restrengthen.[50] After the eye cleared and became surrounded by deep convection, the hurricane reached a secondary peak intensity at Category 3 status at 03:00 UTC on September 5, with maximum sustained winds of 115 mph (185 km/h) and a minimum central pressure of Lua error in Module:Convert at line 1851: attempt to index local 'en_value' (a nil value)..[51] After about 12 hours, Dorian began to gradually weaken as it traveled along the South Carolina coast.[52] The storm fell to Category 1 status by 09:00 UTC on September 6 as a result of increasing wind shear and dry air.[53]

Records

After Dorian rapidly intensified to its peak intensity, it broke numerous intensity records. Dorian is tied with the 1935 Labor Day hurricane, Gilbert, and Wilma for the second-highest wind speed of an Atlantic hurricane at 185 mph (195 km/h),[54][43] which was just below Allen's record wind speed of 190 mph (305 km/h).[55] This intensity made Dorian the strongest hurricane outside of the tropics (>23.5°N)[43], as well as the strongest in the northwestern Bahamas.[33] Dorian's 185 mph (295 km/h) landfalls on Abaco Island and Grand Bahama were the strongest on record for both islands.[43]

See also

References

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  43. ↑ 43.0 43.1 43.2 43.3 Lua error in package.lua at line 80: module 'strict' not found.
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External links


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