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Friday, September 06, 2019, 21:00 CEST



Tropical Cyclone
Caribbeans, USA, Canada
August 24 - September 09, 2019


Satellite image (visible) from Dorian
September 05,
Source: NOAA

DORIAN is the 4th named storm and 1st major hurricane in the atlatic hurricane season in 2019. Its wind speeds reached a maximum of 298 km/h and his minimum core pressure was 910 hPa. So he was a Category 5 hurricane and as such hit the Bahamas. As a Category 4 hurricane it also hit the east coast of the USA. The highest rainfall was registered at 386,3 mm in Pawleys.




Development and trajectory

DORIAN developed from a tropical depression in the tropical Atlantic northeast of the South American coast. Initially visible from 22 August as a thunderstorm cluster on the satellite images, rapid rotation set in and the spiral bands formed. On 24 August DORIAN was classified as a tropical storm. It initially shifted at 20 kph towards the west northwest and reached the West Indies as a tropical storm on 27 August. Then DORIAN shifted to the north and reached category 1 of the Saffir-Simpson scale in the night from 28 to 29 August. At this time it was on the Caribbean Sea about 95 km northwest of Puerto Rico. Its displacement speed of 20 kph was maintained for the time being.

Already one day later he reached category 2 and was located north of the island Turks and Caios. The typical hurricane eye in the centre of the storm was now clearly visible. Its core pressure was 972 hPa, falling tendency, its average wind speed 175 kph, gusts 205 kph. Due to his slowing velocity and the high water temperatures of around 30 C, DORIAN quickly gained energy. A few hours later he reached Category 4 and headed for Bahamas. The core pressure dropped to 925 hPa, his wind speed increased to 225 kph (gusts 230 kph).

DORIANs Trajecotory from 24 August until 09 September Wunderground


DORIAN reached category 5 on the Saffir-Simpson scale on 1st September due to high water temperatures and low wind shear. The core pressure was only 910 hPa, the wind speeds reached more than 300 kph, in gusts 360 kph. At that time the eye was over the Caribbean island of Great Abaco. The displacement speed was only 11 kph and decreased further. On September 2nd DORIAN was almost stationary and stayed more than 48 hours over the Bahamas (center over Grand Bahama). Meanwhile he went through an Eyewall Replacement Cycle, which often leads to a re-intensification after a brief weakening of the storm.

Satellite images from August 27 till September 01: source NASA Worldview
Satellite images from September 02 till September 05: source NASA Worldview
Satellite images from September 05 till September 08: source NASA Worldview


From the 3rd of September the speed of displacement increased again and DORIAN turned off to the north before Florida. At this point it had went down to category 3. The core pressure had increased to 955 hPa, the wind speed had decreased to 175 kph (gusts 215 kph). Until 6 September it remained a Category 3 hurricane and shifted northeast almost parallel to the east coast of the USA and made landfall in North Carolina. Its core pressure rises only slightly. The water temperatures in the Atlantic are still high, so there is still enough energy available to maintain its strength. This results in this remarkably long life span, even in the northern latitudes.
After DORIAN had weakened for a short time to a hurricane of category 1 (145 kph, gusts 193 kph, core pressure 965 hPa), it strengthened on September 7 again to a category 2 hurricane (160 kph, core pressure 953 hPa) and met the Canadian Atlantic province Nova Scotia with this strength. Over the Gulf of St. Lawrence it weakened to category 1 due to the cool sea temperatures and increasing wind shear and grazed Newfoundland with this strength on 8 September. Core pressure rose to 968 hPa and continued to rise to 990 hPa the following day. Wind speeds ranged between 104 kph and 120 kph. It then shifted further west to the northern Atlantic and was downgraded to a tropical storm. Over the coming week DORIAN will undergo an extratropical transition and reach Europe as a storm low.

Observations

Even before DORIAN reached category 5, it brought heavy rainfall. On the Antilles and Puerto Rico this was locally intensified by stagnant precipitation. What is particularly remarkable about DORIAN is its long lifespan (12.5 hurricane days until now) and the very slow rate of displacement in the Bahamas. In 24 hours it shifted by only 40 km. The effects of the heavy precipitation caused by a hurricane were intensified by the stationarity. In 72 hours as much precipitation (more than 750 mm) fell on Abaco Island (Bahamas) as in one year in Karlsruhe (approx. 728 mm).
In addition to the large amounts of precipitation, the storm surges triggered by the enormous winds also led to violent flooding. Besides the 185 mph maximum sustained winds by DORIAN were the strongest on record by any hurricane in the Atlantic basin outside of the tropics (>23.5N). Dorian is he strongest hurricane on record to make landfall in the Bahamas (based on maximum sustained wind) - First Category 5 hurricane on record to make landfall on Grand Bahama Island.

The prediction that DORIAN would make landfall as a Category 3 or 4 hurricane in Florida was not confirmed. However, it moved parallel along the east coast of the USA and almost landfall at Cape Hatteras, Noth Carolina. In addition, his outer cloud bands produced a series of super cells. These in turn produced numerous tornadoes and waterspouts and led to a tornado outbreak in Carolina. The table below shows an overview of precipitation amounts in the USA from September 01 -07. Also the gusts are shown.

Location Precipitation
amount in mm
Pawleys Island (SC)
Wilmington (NC)
Myrtle Beach (SC)
Conway (SC)
Smithgreek (NC)
Lumber River(NC)
McClellanville (SC)
Myrtle Beach (SC)
386.3
382.0
324.4
301.2
288.5
278.4
271.8
265.4
Location Gusts
in kph
Cedar Island (NC)
Buyton/ Hatteras High School (NC)
Oregon Inlet (NC)
Centenary 39 SSE (SC)
Dewees Island (SC)
Fripp Island (SC)
Cheasapeake Light Tower (VA)
Nantucket Shoals Buoy (MA)
177.0
162.5
162.5
157.7
148.0
148.0
133.6
122.3


Data source: Source: NOAA

Damages

Since DORIAN came across the Bahamas as category 5, it left a picture of destruction there. Due to the strong winds and heavy rainfall, to which Abaco Island in particular was exposed, entire houses/cities and regions were completely destroyed. The storm surge increased the amount of water and pushed whole ships into the interior, which ran aground there.
The Leonard M. Thompson International Airport on Great Abaco was completely occupied by the water dimensions. The number of deaths is currently more than 43 and rising. An exact number cannot yet be confirmed.

Damages of DORIAN on the Bahamas and Canada (right): source Wunderground



Text: MG
September 06, 2019


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