Monthly Archives: April 2019

NHC Upgrades Hurricane Michael to Cat. 5

The National Hurricane Center (NHC) upgraded Hurricane Michael to Category 5 on the Saffir-Simpson Scale after it completed and released its post storm analysis on Friday.  NHC does a post storm analysis of every tropical cyclone in its area of responsibility after the end of the hurricane season.  The maximum sustained wind speed at the time of landfall in northwest Florida of Hurricane Michael, which was given originally as 155 m.p.h. (250 km/h), was increased to 160 m.p.h. (260 km/h) after the post storm analysis.  Hurricane Michael becomes one of only four hurricanes to make landfall in the U.S. as a Category 5 hurricane.  The other Category 5 hurricanes to hit the U.S. were the Labor Day Hurricane which hit the Florida Keys in 1935, Hurricane Camille which hit Mississippi in 1969 and Hurricane Andrew which hit south Florida in 1992.

The National Hurricane Center prepares a Tropical Storm Report on every tropical cyclone in its area of responsibility and those reports are available on NHC’s web site.  J. L. Beven II, R. Berg and A. Hagen were the authors of the Tropical Cyclone Report on Hurricane Michael.  They explain in the Tropical Cyclone Report how they arrived at the intensity of Hurricane Michael at landfall.  They analyzed aircraft data including flight level winds and SMFR intensities.  They did an analysis of the Dopper wind velocities observed by the WSR-88D radar at Eglin Air Force Base.  They also considered available data on the surface winds and pressures and satellite derived estimates of the intensity of Hurricane Michael.  Based on analysis of all of that information, they concluded that the intensity of Hurricane Michael when it made landfall in northwest Florida was 160 m.p.h. (260 km/h).  Their full Tropical Cyclone Report on Hurricane Michael is available on NHC’s website at https://www.nhc.noaa.gov/data/tcr/AL142018_Michael.pdf.

Tropical Cyclone Wallace Churns Northwest of Australia

Tropical Cyclone Wallace continued to churn northwest of Australia on Sunday.  At 11:00 p.m. EDT on Sunday the center of Tropical Cyclone Wallace was located at latitude 15.3°S and longitude 116.4°E which put it about 435 miles (700 km) north of Karratha, Australia.  Wallace was moving toward the southwest at 11 m.p.h. (17 km/h).  The maximum sustained wind speed was 65 m.p.h. (105 km/h) and there were wind gusts to 80 m.p.h. (130 km/h).  The minimum surface pressure was 987 mb.

The circulation around Tropical Cyclone Wallace exhibited signs of greater organization on Sunday.  The inner end of a band of showers and thunderstorms wrapped around the southern and western sides of the center of circulation.  More thunderstorms formed in other bands that were revolving around the core of Tropical Cyclone Wallace.  Storms near the core were generating upper level divergence which was pumping mass away to the west and south of the tropical cyclone.  Winds to tropical storm force extended out about 140 miles (220 km) from the center of circulation.

Tropical Cyclone Wallace will move through an environment somewhat favorable for intensification during the next 24 hours.  Wallace will move over water where Sea Surface Temperature is near 28°C.  It will move near the western end of an upper level ridge over northern Australia.  The ridge will produce easterly winds which will cause moderate vertical wind shear.  The shear will limit intensification, but it may not be great enough to prevent Tropical Cyclone Wallace from getting stronger.  Wallace could strengthen into the equivalent of a hurricane/typhoon during the next 24 hours.

The ridge over northern Australia will steer Tropical Cyclone Wallace toward the west-southwest during the next few days.  On its anticipated track Wallace is forecast to remain north of Western Australia.

Tropical Cyclone Wallace Develops North of Western Australia

Tropical Cyclone Wallace developed over the Timor Sea north of Western Australia on Friday.  At 2:00 p.m. EDT on Friday the center of Tropical Cyclone Wallace was located at latitude 11.7°S and longitude 125.7°E which put it about 280 miles (440 km) north-northeast of Kuri Bay, Australia.  Wallace was moving toward the west at 6 m.p.h. (9 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 997 mb.

The Australian Bureau of Meteorology posted a Tropical Cyclone Warning from Kalumburu to Beagle Bay.

More thunderstorms developed near the center of a Tropical Low over the Timor Sea on Friday and the Australian Bureau of Meteorology designated the system as Tropical Cyclone Wallace.  The distribution of thunderstorms in the circulation around Wallace was asymmetrical.  Most of the thunderstorms were occurring west of the center of circulation and in bands in the western half of the tropical cyclone.  Bands in the eastern half of of Tropical Cyclone Wallace consisted primarily of showers and lower clouds.  Winds to tropical storm force extended out about 150 miles (240 km) from the center of circulation.

Tropical Cyclone Wallace was moving north of an upper level ridge.  The ridge was producing strong easterly winds which were causing significant vertical wind shear.  Those winds and the shear were probably the cause of the asymmetrical distribution of thunderstorms.  Storms west of the center of circulation were generating upper level divergence which was pumping mass away to the west of Tropical Cyclone Wallace.

Tropical Cyclone Wallace may move into an area more favorable for intensification during the next day or two.  Wallace could move into an area where the upper level winds are not quite as strong.  Tropical Cyclone Wallace will move over water where the Sea Surface Temperature is near 29°C.  So, if it moves into an area where the shear is less, then Tropical Cyclone Wallace is likely to strengthen.  There is a chance Wallace could intensify into the equivalent of a hurricane/typhoon during the next two or three days.

Tropical Cyclone Wallace will move around the northwestern end of a subtropical ridge over Australia.  The ridge will steer Wallace toward the west-southwest during the next several days.  On its anticipated track the core of Tropical Cyclone Wallace is forecast to stay north of the coast of Western Australia during the next few days.