- Email: [email protected]
A short note on the intensification and extreme rainfall associated with hurricane lane
June 2019
Callaghan
103
A SHORT NOTE ON THE INTENSIFICATION AND EXTREME RAINFALL ASSOCIATED WITH HURRICANE LANE Jeff Callaghan Retired Bureau of Meteorology, Brisbane, Australia
ABSTRACT Hurricanes Lane intensified in the Central Pacific with data from reconnaissance aircraft indicating it reached category 5 intensity on the Saffir-Simpson Hurricane Wind Scale while moving closer to Hawaii. The cyclone weakened as it moved closer to the Hawaiian Islands with its closest approach at 1500UTC 25 August 2018 when 175km south southwest of Honolulu with a central pressure of 995hPa. The impact on Hawaii was mainly record rainfall and the structure of this weather system is examined here to show how the winds turning anticyclonically with height in the lower to middle level troposphere play a crucial role in the intensification of Hurricane Lane to category 5 intensity and the generation of extreme rainfall. Keywords: complete eyewall, record rainfall, floods
1. Introduction
Following a series of studies which related the turning of the winds anticyclonically with height in the lower to middle troposphere with intensification of tropical cyclones and extreme rainfall (Callaghan 2018, 2017a and 2017b, Callaghan and Power 2016, Callaghan and Tory 2014) and Tory 2014), Hurricane Lane (2018) is investigated. Lane reached US category 5 intensity on the Saffir-Simpson Hurricane Wind Scale while moving towards Hawaii. Following on from the investigation into Hurricanes Harvey and Irma (Callaghan 2018) a similar investigation is presented here examining the intensification of Lane and the extreme rainfall on the outer fringes of the hurricane. Here also the Hurricane Research Division (HRD) Doppler radar wind data set is utilized along with radiosonde wind data from the upper atmosphere wind station at Hilo International Airport on the Big Island of Hawaii.
2. Intensification to Category 5
Lane developed from an area of thunderstorms off the Southern Mexican coast on August 11 2018 and was rated by forecasters as a Category 4 Hurricane by 0900UTC August 18 2018 while 3105 km WSW of the southern tip of Baja California. On 19 August Lane developed a weakening trend as it moved into the Central Pacific Basin and by 1500UTC 20 August it had, intensified again into a Category 4 storm. Lane then began another period of intenCorresponding author: Jeff Callaghan, [email protected]
DOI: 10.6057/2019TCRR02.05
sification and data from the NOAA aircraft indicated that at 0420UTC on 22 August 2018 it had reached Category 5 intensity. From its track (see Figure 1) at this time it was well to the south southeast of the Big Island. At 1828UTC 20 August 2018 reconnaissance aircraft obtained Doppler wind observations from Lane (see location in Figure 1) and at the time Lane was intensifying over the previous 6 hours from maximum sustained winds of 56.6m/s to 59.2m/s and went on to intensify to 72m/s over the following 30 hours. Doppler winds (Figure 2) show that at 1828UTC 20 August the ascent region (anticyclonic turning winds with height) in the northern side of Lane dominating the circulation with a relatively small and weak region of descent (cyclonic turning) in the southern region. In other regions there was no coherent turning of the winds in either direction. The dominance of the ascent region helped generate intense convection which we was able to circulate around the eyewall and survive through the weak descent region producing the circular bands of intense convection (red to brown areas) in the microwave series (Figure 3). This follows Reasor et al 2009 who showed that with Hurricane Guillermo (1997) the maximum intensification occurred when the convection was able to circulate entirely around the eyewall to form a complete eyewall. Prior to this the intense convection around Guillermo was confined to the downshear (deep layered 850 to 200hPa shear) left side. The deep layered shear was from the NNW while the 1.5km to 6km (approximately 850 to 500hPa) was from the NW due to a clockwise turning hodograph. This relation-
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Fig. 1. Track of Hurricane Lane where numerical code shows the date, time and category under the Saffir–Simpson hurricane wind scale where 211800Z 4 means 1800UTC 21 August 2018 Category 4. Category 5 intensities are highlighted in red and TS means Tropical Storm intensity.
Fig. 2. Horizontal plots of a composite two real time Doppler radar analyses for Hurricane Lane at 1828UTC 20 August 2018 at 5km elevation (top), 3km elevation (centre) and 1km elevation (bottom). Red wind plot colours denote ascent (winds turning anticyclonic with height) and Black plots indicate descent (winds turning cyclonic with height). From http://www.aoml.noaa.gov/hrd/data_sub/hurr.html
June 2019
Callaghan
Fig. 3. Microwave images (courtesy NRL Monterey) with red to brown areas denoting the most intense convection for 1237UTC 20 August 2018 (left) and 0148UTC 21 August 2018 (right).
ship between the 850 to 500hPa shear and the deep layered shear means that the intense convection originally occurred where the wind direction turned in an anticyclonic fashion from 850hPa up to 500hPa. From the reconnaissance data at the same time the vertical tilt of Lane from 2km to 7km was 5.6km towards the north and the SHIPs wind shear was 1.3m/s from the north. From Chen et al 2006 the SHIPS environmental vertical wind shear is defined as the difference between the mean wind vectors of the 200 and 850hPa levels over an outer region extending from the radius of 200–800 km around the storm centre. Such low tilt and shear favours intensification. A 700hPa isotherm chart (Figure 4) around the same time as the Doppler winds attempts to indicate how the ascent region originates. From Tory 2014 the anticyclonic turning winds relates to warm air advection. The isotherm chart (derived from NCEP/NCAR reanalysis) is course (2.5degree resolution) and couldn’t attempt to simulate the complex interaction between the hurricane and the cold region to its northeast. However it seems likely that the warm air advection results from warm air in the circulation of the hurricane flowing into cooler air to the north. The role of deep convection from warm air advection leading to intensification was explored by Heymsfield et al (2001). Using reconnaissance data, they analysed an intense convective episode in the eyewall of Hurricane Bonnie 1998 and found it was associated with a broad current of subsiding air within the eye producing 3°C of warming between 5 and 6 km relative to the eyewall resulting from deep descent from tropopause height. This leads to the possibility of deep convection near the eyewall of directly providing subsidence warming in the eye. This deep convection episode was generated by warm air advection (Callaghan, J. 2017b).
105
Fig. 4. 700hPa Temperature charts for 1800UTC 20 August 2018 drawn from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis https:// www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html. Solid black circle marks the position of Hurricane Lane.
3. Extreme rainfall
Although Hurricane Lane remained west of the Big Island of Hawaii, tremendous rains battered eastern areas of the island from August 22 to 25. On the Big Island flooding closed numerous roads, multiple landslides occurred and in and around Hilo swollen rivers inundated homes (some were destroyed) and other buildings and cars were abandoned on flooded roads. A rain gauge at Mountain View (19.4 km SSW from Hilo elevation 437metres) recorded 1.32metres of rain mostly between 22 August and 25 August. National Weather Service officials say this total could be the highest tropical cyclone storm total ever recorded in Hawaii. Hilo registered 381mm of rain on Friday 24 August making it the fifthwettest calendar day on record and Hilo’s three-day total of 809mm was the city’s highest total for any three-day period in National Weather Service data going back to 1949. However this falls short of the 1029mm dumped by Hurricane Harvey between August 28 and 30 2017, at Beaumont–Port Arthur, Texas. Figure 5 highlights the 24hour period when extreme rainfall was recorded at Hilo and the rainfall distribution shows that the heaviest rainfall fell on the southeastern slopes of the giant volcanoes Mauna Kea and Mauna Loa. Figure 6 shows the Hilo winds during the extreme rainfall and how the direction changes in an anticyclonic fashion from 850hPa up to 500hPa. Charts at 850hPa and 500hPa during the extreme rainfall (Figure 7) showing the 850hPa high pressure ridge north of the Hawaiian Islands while at 500hPa a pressure ridge extended southwards to the east and then south of the Big Island. This resulted in the winds at Hilo turning in an anti-
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Fig.5. Twenty four hour rainfall (mm) to 0545UTC 25 August 2018.
Fig. 6. Upper winds at Hilo 1200UTC 21 August 2018 (211200) to 1200UTC 25 August 2018 (251200).
cyclonic fashion from 850hPa up to 500hPa.
References
Callaghan, J. 2018: A Short Note on the Rapid Intensification of Hurricanes Harvey and Irma. Tropical Cyclone Research and Review, 7(3), 164-171. Callaghan, J. 2017a: A Diagnostic from Vertical Wind Profiles for Detecting Extreme Rainfall. Tropical Cyclone Research and Review, 6(3-4), 41-54. Callaghan, J. 2017b: Asymmetric Inner Core Convection Leading to Tropical Cyclone Intensification. Tropical Cyclone Research and Review, 6(3-4), 55-66. Callaghan J. and S. B. Power 2016. A vertical wind structure that leads to extreme rainfall and major flooding in southeast Australia, Journal of Southern Hemisphere Earth Systems Science
(2016) 66:380-401. http://www.bom.gov.au/jshess/docs/2016/ Callaghan.pdf Callaghan, J. and K. Tory, 2014: On the Use of a System-Scale Ascent/Descent Diagnostic for Short-Term Forecasting of Tropical Cyclone Development, Intensification and Decay. Tropical Cyclone Research and Review, 3(2), 78-90. Chen S. S. J. A. Knaff and F. D. Marks Jr. 2006: Effects of Vertical Wind Shear and Storm Motion on Tropical Cyclone Rainfall Asymmetries Deduced from TRMM. Monthly Weather Review, 134, 3190- 3207. Heymsfield, G. M., J. B. Halverson, J. Simpson, Lin Tian and P. Bui 2001: ER-2 Doppler Radar Investigations of the Eyewall of Hurricane Bonnie during the Convection and Moisture Experiment-3. Journal of Applied Meteorology, 40(8), 1310– 1330. Tory, K 2014: The turning winds with height thermal advection
June 2019
Callaghan
107
Fig. 7. 850hPa Geopotential height charts (left) and 500hPa Geopotential height charts (right) drawn from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis https:// www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html. Solid black circle marks the position of Hurricane Lane and wind plots are from Hawaiian upper wind stations Lihue (left) and Hilo (right). Top frames are for 0000UTC 23 August 2018, Centre frames are for 0000UTC 24 August 2018 and Lower frames are for 0000UTC 25 August 2018.
rainfall diagnostic: why does it work in the tropics? Australian Meteorological and Oceanographic Journal, 64(3), 231-238. Maclay, K. S., Demaria, M and Vonder Haar T. H. 2008: Tropical Cyclone Inner-Core Kinetic Energy Evolution. Mon. Wea. Rev., 136, 4882-4898.
Reasor, P.D., M. D. Eastin, and J. F. Gamache, 2009: Rapidly Intensifying Hurricane Guillermo (1997). Part I: LowWavenumber Structure and Evolution. Mon. Wea. Rev., 137, 603–631.
Callaghan
103
A SHORT NOTE ON THE INTENSIFICATION AND EXTREME RAINFALL ASSOCIATED WITH HURRICANE LANE Jeff Callaghan Retired Bureau of Meteorology, Brisbane, Australia
ABSTRACT Hurricanes Lane intensified in the Central Pacific with data from reconnaissance aircraft indicating it reached category 5 intensity on the Saffir-Simpson Hurricane Wind Scale while moving closer to Hawaii. The cyclone weakened as it moved closer to the Hawaiian Islands with its closest approach at 1500UTC 25 August 2018 when 175km south southwest of Honolulu with a central pressure of 995hPa. The impact on Hawaii was mainly record rainfall and the structure of this weather system is examined here to show how the winds turning anticyclonically with height in the lower to middle level troposphere play a crucial role in the intensification of Hurricane Lane to category 5 intensity and the generation of extreme rainfall. Keywords: complete eyewall, record rainfall, floods
1. Introduction
Following a series of studies which related the turning of the winds anticyclonically with height in the lower to middle troposphere with intensification of tropical cyclones and extreme rainfall (Callaghan 2018, 2017a and 2017b, Callaghan and Power 2016, Callaghan and Tory 2014) and Tory 2014), Hurricane Lane (2018) is investigated. Lane reached US category 5 intensity on the Saffir-Simpson Hurricane Wind Scale while moving towards Hawaii. Following on from the investigation into Hurricanes Harvey and Irma (Callaghan 2018) a similar investigation is presented here examining the intensification of Lane and the extreme rainfall on the outer fringes of the hurricane. Here also the Hurricane Research Division (HRD) Doppler radar wind data set is utilized along with radiosonde wind data from the upper atmosphere wind station at Hilo International Airport on the Big Island of Hawaii.
2. Intensification to Category 5
Lane developed from an area of thunderstorms off the Southern Mexican coast on August 11 2018 and was rated by forecasters as a Category 4 Hurricane by 0900UTC August 18 2018 while 3105 km WSW of the southern tip of Baja California. On 19 August Lane developed a weakening trend as it moved into the Central Pacific Basin and by 1500UTC 20 August it had, intensified again into a Category 4 storm. Lane then began another period of intenCorresponding author: Jeff Callaghan, [email protected]
DOI: 10.6057/2019TCRR02.05
sification and data from the NOAA aircraft indicated that at 0420UTC on 22 August 2018 it had reached Category 5 intensity. From its track (see Figure 1) at this time it was well to the south southeast of the Big Island. At 1828UTC 20 August 2018 reconnaissance aircraft obtained Doppler wind observations from Lane (see location in Figure 1) and at the time Lane was intensifying over the previous 6 hours from maximum sustained winds of 56.6m/s to 59.2m/s and went on to intensify to 72m/s over the following 30 hours. Doppler winds (Figure 2) show that at 1828UTC 20 August the ascent region (anticyclonic turning winds with height) in the northern side of Lane dominating the circulation with a relatively small and weak region of descent (cyclonic turning) in the southern region. In other regions there was no coherent turning of the winds in either direction. The dominance of the ascent region helped generate intense convection which we was able to circulate around the eyewall and survive through the weak descent region producing the circular bands of intense convection (red to brown areas) in the microwave series (Figure 3). This follows Reasor et al 2009 who showed that with Hurricane Guillermo (1997) the maximum intensification occurred when the convection was able to circulate entirely around the eyewall to form a complete eyewall. Prior to this the intense convection around Guillermo was confined to the downshear (deep layered 850 to 200hPa shear) left side. The deep layered shear was from the NNW while the 1.5km to 6km (approximately 850 to 500hPa) was from the NW due to a clockwise turning hodograph. This relation-
104
Tropical Cyclone Research and Review
Volume 8, No. 2
Fig. 1. Track of Hurricane Lane where numerical code shows the date, time and category under the Saffir–Simpson hurricane wind scale where 211800Z 4 means 1800UTC 21 August 2018 Category 4. Category 5 intensities are highlighted in red and TS means Tropical Storm intensity.
Fig. 2. Horizontal plots of a composite two real time Doppler radar analyses for Hurricane Lane at 1828UTC 20 August 2018 at 5km elevation (top), 3km elevation (centre) and 1km elevation (bottom). Red wind plot colours denote ascent (winds turning anticyclonic with height) and Black plots indicate descent (winds turning cyclonic with height). From http://www.aoml.noaa.gov/hrd/data_sub/hurr.html
June 2019
Callaghan
Fig. 3. Microwave images (courtesy NRL Monterey) with red to brown areas denoting the most intense convection for 1237UTC 20 August 2018 (left) and 0148UTC 21 August 2018 (right).
ship between the 850 to 500hPa shear and the deep layered shear means that the intense convection originally occurred where the wind direction turned in an anticyclonic fashion from 850hPa up to 500hPa. From the reconnaissance data at the same time the vertical tilt of Lane from 2km to 7km was 5.6km towards the north and the SHIPs wind shear was 1.3m/s from the north. From Chen et al 2006 the SHIPS environmental vertical wind shear is defined as the difference between the mean wind vectors of the 200 and 850hPa levels over an outer region extending from the radius of 200–800 km around the storm centre. Such low tilt and shear favours intensification. A 700hPa isotherm chart (Figure 4) around the same time as the Doppler winds attempts to indicate how the ascent region originates. From Tory 2014 the anticyclonic turning winds relates to warm air advection. The isotherm chart (derived from NCEP/NCAR reanalysis) is course (2.5degree resolution) and couldn’t attempt to simulate the complex interaction between the hurricane and the cold region to its northeast. However it seems likely that the warm air advection results from warm air in the circulation of the hurricane flowing into cooler air to the north. The role of deep convection from warm air advection leading to intensification was explored by Heymsfield et al (2001). Using reconnaissance data, they analysed an intense convective episode in the eyewall of Hurricane Bonnie 1998 and found it was associated with a broad current of subsiding air within the eye producing 3°C of warming between 5 and 6 km relative to the eyewall resulting from deep descent from tropopause height. This leads to the possibility of deep convection near the eyewall of directly providing subsidence warming in the eye. This deep convection episode was generated by warm air advection (Callaghan, J. 2017b).
105
Fig. 4. 700hPa Temperature charts for 1800UTC 20 August 2018 drawn from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis https:// www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html. Solid black circle marks the position of Hurricane Lane.
3. Extreme rainfall
Although Hurricane Lane remained west of the Big Island of Hawaii, tremendous rains battered eastern areas of the island from August 22 to 25. On the Big Island flooding closed numerous roads, multiple landslides occurred and in and around Hilo swollen rivers inundated homes (some were destroyed) and other buildings and cars were abandoned on flooded roads. A rain gauge at Mountain View (19.4 km SSW from Hilo elevation 437metres) recorded 1.32metres of rain mostly between 22 August and 25 August. National Weather Service officials say this total could be the highest tropical cyclone storm total ever recorded in Hawaii. Hilo registered 381mm of rain on Friday 24 August making it the fifthwettest calendar day on record and Hilo’s three-day total of 809mm was the city’s highest total for any three-day period in National Weather Service data going back to 1949. However this falls short of the 1029mm dumped by Hurricane Harvey between August 28 and 30 2017, at Beaumont–Port Arthur, Texas. Figure 5 highlights the 24hour period when extreme rainfall was recorded at Hilo and the rainfall distribution shows that the heaviest rainfall fell on the southeastern slopes of the giant volcanoes Mauna Kea and Mauna Loa. Figure 6 shows the Hilo winds during the extreme rainfall and how the direction changes in an anticyclonic fashion from 850hPa up to 500hPa. Charts at 850hPa and 500hPa during the extreme rainfall (Figure 7) showing the 850hPa high pressure ridge north of the Hawaiian Islands while at 500hPa a pressure ridge extended southwards to the east and then south of the Big Island. This resulted in the winds at Hilo turning in an anti-
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Tropical Cyclone Research and Review
Volume 8, No. 2
Fig.5. Twenty four hour rainfall (mm) to 0545UTC 25 August 2018.
Fig. 6. Upper winds at Hilo 1200UTC 21 August 2018 (211200) to 1200UTC 25 August 2018 (251200).
cyclonic fashion from 850hPa up to 500hPa.
References
Callaghan, J. 2018: A Short Note on the Rapid Intensification of Hurricanes Harvey and Irma. Tropical Cyclone Research and Review, 7(3), 164-171. Callaghan, J. 2017a: A Diagnostic from Vertical Wind Profiles for Detecting Extreme Rainfall. Tropical Cyclone Research and Review, 6(3-4), 41-54. Callaghan, J. 2017b: Asymmetric Inner Core Convection Leading to Tropical Cyclone Intensification. Tropical Cyclone Research and Review, 6(3-4), 55-66. Callaghan J. and S. B. Power 2016. A vertical wind structure that leads to extreme rainfall and major flooding in southeast Australia, Journal of Southern Hemisphere Earth Systems Science
(2016) 66:380-401. http://www.bom.gov.au/jshess/docs/2016/ Callaghan.pdf Callaghan, J. and K. Tory, 2014: On the Use of a System-Scale Ascent/Descent Diagnostic for Short-Term Forecasting of Tropical Cyclone Development, Intensification and Decay. Tropical Cyclone Research and Review, 3(2), 78-90. Chen S. S. J. A. Knaff and F. D. Marks Jr. 2006: Effects of Vertical Wind Shear and Storm Motion on Tropical Cyclone Rainfall Asymmetries Deduced from TRMM. Monthly Weather Review, 134, 3190- 3207. Heymsfield, G. M., J. B. Halverson, J. Simpson, Lin Tian and P. Bui 2001: ER-2 Doppler Radar Investigations of the Eyewall of Hurricane Bonnie during the Convection and Moisture Experiment-3. Journal of Applied Meteorology, 40(8), 1310– 1330. Tory, K 2014: The turning winds with height thermal advection
June 2019
Callaghan
107
Fig. 7. 850hPa Geopotential height charts (left) and 500hPa Geopotential height charts (right) drawn from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis https:// www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html. Solid black circle marks the position of Hurricane Lane and wind plots are from Hawaiian upper wind stations Lihue (left) and Hilo (right). Top frames are for 0000UTC 23 August 2018, Centre frames are for 0000UTC 24 August 2018 and Lower frames are for 0000UTC 25 August 2018.
rainfall diagnostic: why does it work in the tropics? Australian Meteorological and Oceanographic Journal, 64(3), 231-238. Maclay, K. S., Demaria, M and Vonder Haar T. H. 2008: Tropical Cyclone Inner-Core Kinetic Energy Evolution. Mon. Wea. Rev., 136, 4882-4898.
Reasor, P.D., M. D. Eastin, and J. F. Gamache, 2009: Rapidly Intensifying Hurricane Guillermo (1997). Part I: LowWavenumber Structure and Evolution. Mon. Wea. Rev., 137, 603–631.