Hurricane Hernan (2008)

Infobox Hurricane
Name=Hurricane Hernan
Type=Hurricane
Year=2008
Basin=EPac
Image location=Hernan 09 aug 2008 1900Z.jpg


Formed=August 6, 2008
Dissipated=August 12, 2008
1-min winds=105
Pressure=956
Da

Fatalities=None
Areas=No land areas
Hurricane season=2008 Pacific hurricane season

Hurricane Hernan was the ninth tropical depression, eighth named storm, fifth hurricane, and first major hurricane of the 2008 Pacific hurricane season. Hernan developed out of a tropical wave that formed off the south-west coast of Mexico on July 31. Over the next several days, the wave moved erratically before being declared Tropical Depression Nine-E on August 6. The depression quickly became Tropical Storm Hernan later that day. Hernan steadily intensified over the next two days and was upgraded to a hurricane on the morning of August 8. Hernan continued to intensify and became the first major hurricane—a storm with winds of 111 mph (178 km/h) or higher—of the season on August 9. After reaching major hurricane status, Hernan steadily weakened to a minimal hurricane. The weakening continued and Hernan was further downgraded to a tropical storm on August 11. As Hernan moved over cold waters, the convection associated with the storm dissipated and Hernan weakened to a tropical depression. By the morning of August 12, almost all of the convection associated with Hernan had dissipated and the system was declared a remnant low-pressure area.

Meteorological history

Late on July 31, a well-defined area of low pressure developed into a tropical wave while located to the south-west of Mexico. [cite web|author=NWS|title=Tropical Weather Discussion July 31, 2008 21Z|year=2008|publisher=National Hurricane Center|accessdate=2008-09-27|url=ftp://ftp.met.fsu.edu/pub/weather/tropical/Pac-Dis/2008073121.AXPZ20] The wave became less organized over the next two days as it slowly moved towards the north-northwest. On August 4, the wave became disorganized due to moderate wind shear. [cite web|author=NWS|title=Tropical Weather Discussion August 4, 2008 09Z|year=2008|publisher=National Hurricane Center|accessdate=2008-09-27|url=ftp://ftp.met.fsu.edu/pub/weather/tropical/Pac-Dis/2008080409.AXPZ20] The wave became better organized throughout the day, and cyclonic turning was noted. [cite web|author=NWS|title=Tropical Weather Discussion August 5, 2008 15Z|year=2008|publisher=National Hurricane Center|accessdate=2008-10-04|url=ftp://ftp.met.fsu.edu/pub/weather/tropical/Pac-Dis/2008080416.AXPZ20] Strong convection also began to develop and slow development was forecast over the next 36 49 hours. [cite web|author=NWS|title=Tropical Weather Discussion August 4, 2008 21Z|year=2008|publisher=National Hurricane Center|accessdate=2008-09-27|url=ftp://ftp.met.fsu.edu/pub/weather/tropical/Pac-Dis/2008080422.AXPZ20] On August 5, a banding feature began to develop as convection continued to persist around the center of the wave. [cite web|author=NWS|title=Tropical Weather Discussion August 5, 2008 21Z|year=2008|publisher=National Hurricane Center|accessdate=2008-09-27|url=ftp://ftp.met.fsu.edu/pub/weather/tropical/Pac-Dis/2008080522.AXPZ20] On the morning of August 6, a Tropical Cyclone Formation Alert was issued for the wave, as development of the system was anticipated over the next several days. [cite web|author=NWS|title=Tropical Weather Discussion August 6, 2008 03Z|year=2008|publisher=National Hurricane Center|accessdate=2008-09-27|url=ftp://ftp.met.fsu.edu/pub/weather/tropical/Pac-Dis/2008080603.AXPZ20] Later in the day, the National Hurricane Center determined that the system had developed enough convection to be declared "Tropical Depression Nine-E" while located 810 mi (1300 km) to the west of Cabo San Lucas, Mexico.cite web|author=Knabb|title=Tropical Depression Nine-E Public Advisory One|year=2008|publisher=National Hurricane Center|accessdate=2008-08-30|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.public.001.shtml?]

Tropical Depression Nine-E was being influenced by a high pressure area located over Mexico, causing it to move at a quick pace of 16 mph (26 km/h) to the north-west. The depression was upgraded to "Tropical Storm Hernan" overnight as the storm became more organized. Although Hernan was located over warm waters, moderate wind shear prevented the storm from intensifying quickly as it continued towards the west-northwest at a slower pace. [cite web|author=Brown|title=Tropical Storm Hernan Discussion Two|year=2008|publisher=National Hurricane Center|accessdate=2008-08-31|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.002.shtml?] Hernan continued to slowly become better organized throughout the night but was still being impaired by northeasterly vertical wind shear during the early morning hours on August 7. [cite web|author=Pasch|title=Tropical Storm Hernan Discussion Three|year=2008|publisher=National Hurricane Center|accessdate=2008-09-25|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.003.shtml?] Wind shear continued to impair Hernan through the morning and none of the forecast models, save the GFDL, forecast Hernan to become a hurricane. [cite web|author=Avila|title=Tropical Storm Hernan Discussion Four|year=2008|publisher=National Hurricane Center|accessdate=2008-09-25|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.004.shtml?]

In the early afternoon, an eye feature began to form, prompting the NHC to state that Hernan was nearing hurricane status. [cite web|author=Knabb|title=Tropical Storm Hernan Discussion Five|year=2008|publisher=National Hurricane Center|accessdate=2008-09-25|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.005.shtml?] However, by the nighttime hours, a microwave satellite found that the center of Hernan was located to the west-southwest of the eye feature, and the intensification ceased for the rest of the day and into the morning of August 8. [cite web|author=Beven|title=Tropical Storm Hernan Discussion Six|year=2008|publisher=National Hurricane Center|accessdate=2008-09-25|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.006.shtml?] [cite web|author=Avila|title=Tropical Storm Hernan Discussion Seven|year=2008|publisher=National Hurricane Center|accessdate=2008-09-25|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.007.shtml?] Later in the morning, the center of Hernan was determined to be located underneath the eye and was determined to have become a hurricane, the fifth of the season, at 8 a.m. (PST) on August 8. [cite web|author=Knabb/Kimberlain|title=Hurricane Hernan Discussion Eight|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.008.shtml?] Throughout the day, the eye became better defined, indicating that Hernan was intensifying. The moderate northeasterly wind shear had already begun to diminish, leading forecasters to show Hernan peaking as a category two hurricane overnight. [cite web|author=Kimberlain/Brown|title=Hurricane Hernan Discussion Nine|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.009.shtml?] That night, the eye was determined to be 30 mi (50 km), though cloud-filled. The convection surrounding the eye also became more intense. [cite web|author=Beven|title=Hurricane Hernan Discussion Ten|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.010.shtml?]

Early on August 9, Hernan was upgraded to a category two hurricane, with winds of 100 mph (155 km/h). Convection around the eye continued become more symmetrical, though the National Hurricane Center had stated that Hernan had most likely reached its peak intensity or was very close to doing so. [cite web|author=Rhome|title=Hurricane Hernan Discussion Eleven|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.011.shtml?] Hernan continued to become better organized throughout the morning, and the eye suddenly became better defined and deep convection formed around the eye. Due to the sudden increase in organization, Hernan was upgraded to a major hurricane, the first of the season, with winds of 120 mph (195 km/h), making it the strongest storm in the 2008 Pacific hurricane season until October 8, when Hurricane Norbert reached an intensity of 125 mph (200 km/h) and a pressure of 952 mbar (hPa; 28.11 inHg). [cite web|author=Rhome|title=Hurricane Norbert Public Advisory Nineteen|year=2008|publisher=National Hurricane Center|accessdate=2008-10-08|url=http://www.nhc.noaa.gov/archive/2008/ep15/ep152008.public.019.shtml?] The intensity of Hernan was uncertain, as there was some difference between intensity estimates. The estimates ranged from 117 mph (192 km/h) to 132 mph (212 km/h). [cite web|author=Knabb|title=Hurricane Hernan Discussion Twelve|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.012.shtml?] Hernan maintained its appearance through the early afternoon, and it was stated that the peak intensity of the storm may have been 125 mph (205 km/h). [cite web|author=Brown|title=Hurricane Hernan Discussion Thirteen|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.013.shtml?] In the late afternoon, Hernan moved over cooler waters and started to weaken. The eye contracted slightly to 25 miles (35 km). Although the eye remained well defined, cloud tops around the eye warmed and outflow to all the southwestern semi-circle was poor. [cite web|author=Beven|title=Hurricane Hernan Discussion Fourteen|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.014.shtml?]

Hernan rapidly weakened overnight and was barely a category two in the early hours of August 10 as it moved over cooler waters. However, the eyewall remained intact throughout the night. [cite web|author=Rhome|title=Hurricane Hernan Discussion Fifteen|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.015.shtml?] Later in the morning, weakening slowed and Hernan was downgraded to a strong category one. The western portion of the eyewall had begun to erode due to the cooling waters. [cite web|author=Pasch|title=Hurricane Hernan Discussion Sixteen|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.016.shtml?] The erosion of the eyewall was later found to be caused by an eyewall replacement cycle that rapidly completed itself during the afternoon. The diameter of the eye remained 25 miles (35 km) wide, but Hernan continued to slowly weaken. [cite web|author=Knabb|title=Hurricane Hernan Discussion Seventeen|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.017.shtml?] The newly formed eye began to shrink and deteriorate through the early afternoon but Hernan briefly stopped weakening. [cite web|author=Blake|title=Hurricane Hernan Discussion Eighteen|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.018.shtml?] The weakening trend continued again during the night of August 10 as the cloud tops warmed. [cite web|author=Rhome|title=Hurricane Hernan Discussion Nineteen|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.019.shtml?] Once more, the weakening stopped as a strong burst of convection around the center of the storm appeared. Hernan's strong circulation allowed it to maintain hurricane status over 24°C waters. [cite web|author=Berg/Pasch|title=Hurricane Hernan Discussion Twenty|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.020.shtml?]

Early on August 11, the upper-level and lower-level circulations of Hernan began to separate, and the storm was downgraded to a tropical storm. [cite web|author=Stewart/Pasch|title=Tropical Storm Hernan Discussion Twenty-One|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.021.shtml?] Slow weakening continued through the morning and afternoon as convection diminished around the center of the storm. [cite web|author=Blake|title=Tropical Storm Hernan Discussion Twenty-Two|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.022.shtml?] By the early afternoon, almost all of the deep convection dissipated as Hernan continued to weaken. [cite web|author=Rhome|title=Tropical Storm Hernan Discussion Twenty-Three|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.023.shtml?] Convection continued to diminish as Hernan traveled over 23°C water and was barely holding on to tropical storm status. [cite web|author=Berg/Brown|title=Tropical Storm Hernan Discussion Twenty-Four|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.024.shtml?] By the morning of August 12, only a small area of tropical storm force winds remained with Hernan. Only a swirl of clouds remained and the storm was barely a full tropical system. [cite web|author=Berg/Brown|title=Tropical Storm Hernan Discussion Twenty-Five|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.025.shtml?] Later that morning, Hernan had degenerated into a remnant low and the final advisory was issued by the National Hurricane Center. [cite web|author=Blake|title=Remnant Low Hernan Discussion Twenty-Six|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/archive/2008/ep09/ep092008.discus.026.shtml?]

Impact and naming

The storm never approached land during its lifespan, and no damage or casualties were reported. When Tropical Depression Nine-E was upgraded to Tropical Storm Hernan, it was the fifth time that the name was used for a tropical cyclone in the Eastern Pacific. Hurricane Hernan was used previously in 1984, 1990, 1996, and 2002. [cite web|author=NHC|title=Eastern Pacific Best Tracks, 1949-2007|year=2008|publisher=National Hurricane Center|accessdate=2008-09-26|url=http://www.nhc.noaa.gov/tracks1949to2007_epa.txt]

See also

*2008 Pacific hurricane season
*List of Pacific hurricanes

References