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Hurricane Flora
Grayscale photograph of a radar scope showing the structure of Hurricane Flora
Radar image of Flora over the Sargasso Sea as viewed from the USS Albany on October 9
Meteorological history
FormedSeptember 28, 1963 (1963-09-28)
ExtratropicalOctober 12, 1963
DissipatedOctober 17, 1963 (1963-10-17)
Category 4 major hurricane
1-minute sustained (SSHWS/NWS)
Highest winds150 mph (240 km/h)
Lowest pressure933 mbar (hPa); 27.55 inHg
Overall effects

Part of the 1963 Atlantic hurricane season

Hurricane Flora

Meteorological history

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Map plotting the storm's track and intensity, according to the Saffir–Simpson scale
Map key
  Tropical depression (≤38 mph, ≤62 km/h)
  Tropical storm (39–73 mph, 63–118 km/h)
  Category 1 (74–95 mph, 119–153 km/h)
  Category 2 (96–110 mph, 154–177 km/h)
  Category 3 (111–129 mph, 178–208 km/h)
  Category 4 (130–156 mph, 209–251 km/h)
  Category 5 (≥157 mph, ≥252 km/h)
  Unknown
Storm type
triangle Extratropical cyclone, remnant low, tropical disturbance, or monsoon depression

The tropical wave that ultimately spawned Hurricane Flora moved off the coast of West Africa sometime late on September 23 or early September 24.[1]: 222 [2]: 3 [a] The disturbance gradually became better organized as it moved west across the tropical Atlantic.[1]: 222  Imagery from the TIROS-7 satellite captured the developing system on September 26 in the vicinity of 11°30′N 35°00′W / 11.5°N 35.0°W / 11.5; -35.0, revealing a large and complex cluster of clouds.[2]: 3 [3]: 133  Two disturbances comprising the complex were detected by the TIROS-7 satellite, though it is unclear which particular disturbance became Flora.[1]: 223  While the United States Weather Bureau contemporaneously believed to have formed on September 26, a reanalysis of the official Atlantic hurricane database by the Hurricane Research Division (HRD) determined that the storm became on September 28, 48 hours later than initially assessed, on account of the incipient disturbance's lack of organization in both the September 26 TIROS-7 imagery and a subsequent image taken on September 27.[1]: 223 [4] Weather observations were scant in the vicinity of Flora around the time it became a tropical depression,[3]: 133  preventing a more accurate determination of Flora's genesis. [5]: 20  However, a KLM jet airliner en route to Paramaribo, Suriname, encountered disturbed weather east of the Lesser Antilles on September 28, prompting the Weather Bureau office in San Juan, Puerto Rico, to request special weather observations from ships in the area the next day and schedule a aerial reconnaissance mission into the storm for September 30.[2]: 3 [3]: 133  Retrospective analyses of Flora indicate that it reached tropical storm intensity on September 29.[6][1]: 224  Delayed ship reports documented gale-force winds and low pressures in the vicinity of Flora between September 29–30.[3]: 133  Flora reached hurricane intensity east of the Lesser Antilles by 00:00 UTC on September 30.[1]: 224 [6]

Aircraft hurricane reconnaissance first intercepted the center of Flora around 120 mi (190 km) east of Trinidad at 14:07 UTC on September 30, finding a well-defined eye surrounded by an eyewall spanning 8 mi (13 km) across within the compact hurricane.[1]: 225 [2]: 3 [3]: 133  The flight also assessed winds exceeding the hurricane-force threshold and a central air pressure of 994 mbar (hPa; 29.35 inHg). A summary of the 1963 Atlantic hurricane season authored by Weather Bureau staff and published in the Monthly Weather Review described the mission's observations as "[indicating] that hurricane Flora was the most concentrated and best organized tropical cyclone of the past two years."[3]: 133  Hurricane Flora rapidly intensified as it traversed the Windward Islands throughout September 30. The center of the hurricane made landfall on Tobago at around 18:00 UTC that day. A minimum air pressure of 974 mbar (hPa; 28.76 inHg) was registered at Crown Point, Tobago, which when reconciled with Flora's size, location, and forward speed suggested maximum sustained winds of around 105 mph (165 km/h).[1]: 226  The center of Flora passed roughly 30 mi (48 km) south of Grenada as the hurricane entered the southeastern Caribbean Sea.[2]: 3 

Grayscale radar image of the hurricane
Radar image of Flora on October 2 as observed by U.S. Navy aircraft reconnaissance[7]: 30 

Within the southeastern Caribbean Sea, Flora took a steady course towards Haiti's Tiburon Peninsula that curved progressively northwards with time. The hurricane's rate of intensification on October 1 had become more gradual, though the storm was continuing to strengthen. However, Flora began to strengthen quickly between October 2–3, with periodic aircraft reconnaissance missions finding increasing winds and deepening air pressures.[1]: 226 [3]: 134  Flight-level winds reaching 167 mph (269 km/h) were recorded by reconnaissance missions on both October 2 and October 3.[3]: 134  The HRD reanalysis estimated that Flora became a major hurricane by around 06:00 UTC on October 2,[b] with Flora's winds continuing to increase before reaching a peak of around 150 mph (240 km/h) by 18:00 UTC on October 4; this intensity is equivalent to a Category 4 hurricane on the modern Saffir–Simpson hurricane wind scale. Based on aircraft reconnaissance data, Flora had a minimum central air pressure of around 933 mbar (hPa; 27.55 inHg) at the time of its peak strength.[1]: 227–229 [6] The hurricane slowed its forward course and began moving more towards the north-northwest on October 3,[2]: 3  leading to a landdfall on southwestern Haiti near Côtes-de-Fer at 01:00 UTC on October 4.[1]: 231 [3]: 134  While the HRD reanalysis assessed that Flora made landfall at its peak intensity, the eight-hour gap between landfall and the preceding aircraft reconnaissance mission meant that Flora may have been considerably stronger than estimated at its Haitian landfall.[1]: 231  Flora traversed the Tiburon Peninsula in roughly two hours before emerging into the Windward Passage. The hurricane subsequently made landfall on eastern Cuba approximately 30 mi (48 km) east of Guantanamo Bay at around 18:00 UTC on October 4 with maximum sustained winds estimated at 120 mph (195 km/h);[1]: 231  this intensity is equivalent to a Category 3 hurricane on the Saffir–Simpson scale.[9]: 4189 

Changing weather conditions over the United States in early October 1964 were consequential in shaping Flora's trajectory leading up to and after the hurricane's landfalls on Haiti and Cuba. Although Flora's northward curve was spurred by the presence of a trough off the U.S. East Coast,[c] the subsequent northward retreat of the trough and strengthening ridging over the eastern U.S. caused Flora to slowly curve west between October 5–7. Additional areas of high pressure to Flora's west and east prevented the hurricane from moving away from the region, resulting in Flora lingering near or over eastern Cuba for several days.[2]: 3 [3]: 134–135  While the hurricane's winds diminished somewhat due to Flora's persistent interaction with land, the storm maintained a strong intensity due in part to a conducive atmospheric environment and the presence of moist tropical air atop the warm waters surrounding Cuba.[2]: 3  The hurricane also grew during its traversal of eastern Cuba, with its radius of outermost closed isobar expanding nearly three-fold. On October 6, Flora moved over the Gulf of Guacanayabo and likely restrengthened.[1]: 233  At around 00:00 UTC on October 7, the center of Flora again moved ashore Cuba, this time a few miles west of Santa Cruz del Sur, with estimated maximum sustained winds of 100 mph (155 km/h).[1]: 233  A strengthening anticyclone over the Gulf of Mexico stopped Flora's slow westward course on October 7. Concurrently, the passage of two troughs off the U.S. East Coast and The Bahamas caused Flora to curve east and later northeast over the same regions of Cuba previously traversed by the hurricane.[3]: 135  Between October 7–8, Flora's winds weakened to tropical storm intensity.[2]: 3  However, Flora promptly intensified after reemerging into the Atlantic Ocean near Gibara along the northern Cuban coast after 12:00 UTC on October 8, regaining hurricane intensity six hours later.[1]: 235 

Now moving more steadily towards the northeast, the center of Flora passed over Mayaguana at around 06:00 UTC on October 9 with sustained winds of around 100 mph (155 km/h). A minimum air pressure of 977 mbar (hPa; 28.85 inHg) was recorded on the island within Flora's eye. The hurricane continued to intensify after leaving the Bahamas, with sustained winds topping out at 110 mph (175 km/h).[1]: 236 [6] Accelerating northeast,[1]: 237  Flora passed southeast of Bermuda on October 10 and began losing its tropical characteristics as it moved over the cooler waters of the mid-latitude Atlantic.[2]: 3 [1]: 239  The occurrence of frontogenesis by around 00:00 UTC on October 12 signaled the completion of Flora's transition into an extratropical cyclone. Although Flora weakened during this period, ships in the storm's vicinity observed hurricane-force winds.[1]: 239  Remaining a strong extratropical cyclone, the remnants of Flora progressed northeast and meandered near the Denmark Strait between October 15–17, gradually weakening before being absorbed by a stronger extratropical cyclone.[1]: 240 

Preparations and impact

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Deadliest Atlantic hurricanes
Rank Hurricane Season Fatalities
1  ?  "Great Hurricane" 1780 22,000–27,501
2  5  Mitch 1998 11,374+
3  2  Fifi 1974 8,210–10,000
4  4  "Galveston" 1900 8,000–12,000
5  4  Flora 1963 7,193
6  ?  "Pointe-à-Pitre" 1776 6,000+
7  5  "Okeechobee" 1928 4,112+
8  ?  "Newfoundland" 1775 4,000–4,163
9  3  "Monterrey" 1909 4,000
10  4  "San Ciriaco" 1899 3,855

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Windward Islands

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Grayscale radar image of Flora with the positions of islands labeled
Radar image of Flora passing over Tobago on September 30

Hispaniola

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Jamaica

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Cuba

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The Bahamas and Florida

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Aftermath

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Notes

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  1. ^ For consistency, all dates and times are based on Coordinated Universal Time.
  2. ^ A major hurricane is a storm that ranks as Category 3 or higher on the Saffir–Simpson hurricane wind scale.[8]
  3. ^ The recurring presence of a trough off the U.S. East Coast turned hurricanes Arlene, Beulah, and Debra away from the contiguous U.S. earlier in the year.[3]: 134 

References

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  1. ^ a b c d e f g h i j k l m n o p q r s t u Delgado, Sandy; Landsea, Chris (November 2019). "1963 Atlantic Hurricane Database Reanalysis". [HURDAT Meta-Data, 1961-1965 revisions] (PDF). Miami, Florida: Atlantic Oceanographic and Meteorological Laboratory Hurricane Research Division. pp. 220–241. Retrieved July 31, 2023.
  2. ^ a b c d e f g h i j "Hurricane Flora, September 30–October 12, 1963". United States Weather Bureau. Retrieved July 31, 2023. The individual pages of this report are each respectively located at the following links:
  3. ^ a b c d e f g h i j k l Dunn, Gordon E.; Moore, Paul L.; Clark, Gilbert B.; Frank, Neil L.; Hill, Elbert C.; Kraft, Raymond H.; Sugg, Arnold L. (March 1964). "The Hurricane Season of 1963". Monthly Weather Review. 92 (3). American Meteorological Society: 128–138. doi:10.1175/1520-0493(1964)092<0128:THSO>2.3.CO;2.
  4. ^ Delgado, Sandy; Landsea, Christopher W.; Willoughby, Hugh (June 2018). "Supplemental Material". Journal of Climate. 31 (11). doi:10.1175/JCLI-D-15-0537.s1.
  5. ^ Frank, Neil L. (February 1964). "The 1963 Hurricane Season". Weatherwise. 17 (1). Taylor & Francis: 16–23. doi:10.1080/00431672.1964.9927014.
  6. ^ a b c d "1963 Major Hurricane FLORA (1963272N09314)". University of North Carolina–Asheville. Retrieved July 31, 2023.
  7. ^ Allison, Lewis J.; Thompson, Harold P. (June 1966). Tiros VII Infrared Radiation Coverage of the 1963 Atlantic Hurricane Season with Supporting Television and Conventional Meteorological Data (PDF) (NASA Technical Note). Washington, D.C.: Goddard Space Flight Center, NASA. Retrieved July 31, 2023.
  8. ^ "Hurricanes Frequently Asked Questions". Atlantic Oceanographic & Meteorological Laboratory. Miami, Florida: National Oceanic and Atmospheric Administration. June 1, 2023. The Saffir-Simpson Scale. Retrieved June 20, 2023.
  9. ^ Delgado, Sandy; Landsea, Christopher W.; Willoughby, Hugh (June 2018). "Reanalysis of the 1954–63 Atlantic Hurricane Seasons". Journal of Climate. 31 (11): 4177–4192. doi:10.1175/JCLI-D-15-0537.1.
  10. ^ Green, Raymond A. (January 1964). "The Weather and Circulation of October 1963". Monthly Weather Review. 92 (1). American Meteorological Society: 37–42. doi:10.1175/1520-0493(1964)092<0037:TWACOO>2.3.CO;2.