Monthly Archives: March 2017

Tropical Cyclone Blanche Strengthens Near Coast of Western Australia

Tropical Cyclone Blanche strengthened on Sunday as it moved over the Timor Sea toward the coast of Western Australia.  At 7:00 p.m. EST on Sunday the center of Tropical Cyclone Blanche was located at latitude 14.0°S and longitude 128.2°E which put it about 100 miles (165 km) north of Wyndham, Australia.  Blanche was moving toward the southwest at 11 m.p.h. (17 km/h).  The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 80 m.p.h. (130 km/h).  The minimum surface pressure was 988 mb.

The inner core of Tropical Cyclone Blanche became more organized on Sunday.  A band of thunderstorms wrapped about two thirds of the way around the southern and western portions of the center.  The band has the appearance of a partial eyewall.  The strongest winds are occurring in the band near the center.  The thunderstorms are generating upper level divergence which is pumping out mass to the west and southeast of the Tropical Cyclone Blanche.  The upper level divergence allowed the surface pressure to decrease and the wind speed to increase.

Tropical Cyclone Blanche will be over the Timor Sea for a few more hours.  It will be in an environment that is favorable for intensification during that time.  Blanche will move over water where the Sea Surface Temperature is near 29°C.  An upper level ridge east of Blanche is producing northerly winds which are blowing toward the tropical cyclone.  The winds are causing moderate vertical wind shear, but the shear was not strong enough to prevent intensification on Sunday.  Tropical Cyclone Blanche could intensify a little more before it makes landfall.

A subtropical ridge is steering Tropical Cyclone Blanche toward the southwest and that general motion is expected to continue.  On its anticipated track Tropical Cyclone Blanche will make landfall on the coast of Western Australia northwest of Wyndham in a few hours.  Blanche will bring gusty winds and some storm surge to the coast.  It will cause locally heavy rain and the potential for flooding as it moves inland.

Tropical Cyclone Enawo Intensifies Into Equivalent of a Hurricane

Tropical Cyclone Enawo intensified into the equivalent of a hurricane/typhoon on Saturday.  At 10:00 p.m. EST on Saturday the center of Tropical Cyclone Enawo was located at latitude 13.9°S and longitude 56.3°E which put it about 475 miles (765 km) north of St. Denis, La Reunion.  Enawo was moving toward the south at 2 m.p.h. (3 km/h).  The maximum sustained wind speed was 80 m.p.h. (130 km/h) and there were wind gusts to 95 m.p.h. (155 km/h).  The minimum surface pressure was 979 mb.

A primary rainband wrapped around the center of circulation and there was evidence of an eye on microwave satellite imagery.  A broken ring of thunderstorms surrounded the eye.  Additional bands of thunderstorms were rotating around the core of the circulation.  Thunderstorms near the center of circulation were generating upper level divergence which was pumping out mass in all directions.  The circulation of Tropical Cyclone Enawo is relatively small and winds to tropical storm force only extended out about 100 miles (160 km) from the center.

Tropical Cyclone Enawo will move through an environment very favorable for intensification during the next several days.  It will move over water where the Sea Surface Temperature is near 30°C.  The upper level winds are weak and there is little vertical wind shear.  Tropical Cyclone Enawo will continue to intensify and it could intensify rapidly for a time.  Tropical Cyclone Enawo is likely to become the equivalent of a major hurricane within 48 hours.

Tropical Cyclone Enawo was in an area where the steering currents were weak and it did not move much on Saturday.  A subtropical ridge east of Enawo is forecast to strengthen and extend westward.  When the ridge strengthens, it is expected to steer Tropical Cyclone Enawo toward the west-southwest.  On its anticipated track Tropical Cyclone Enawo could approach the coast of northeast Madagascar in 48 to 72 hours.  It could be a strong, dangerous tropical cyclone at that time.

Tropical Cyclone Blanche Forms Northwest of Darwin

Tropical Cyclone Blanche formed northwest of Darwin, Australia over the Timor Sea late on Saturday.  At 10:00 p.m. EST on Saturday the center of Tropical Cyclone Blanche was located at latitude 11.9°S and longitude 130.3°E which put it about 55 miles (85 km) northwest of Darwin, Australia.  Blanche was moving toward the southwest at 7 m.p.h. (12 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 993 mb.

An area of low pressure moved north of the Northern Territory over the Arafura Sea during the past few days.  The low exhibited enough organization for the Australian Bureau of Meteorology to designate it as a tropical low.  The center of the low moved across Melville Island and Bathhurst Island earlier today.  More and stronger thunderstorms began to form closer to the center after it moved over the Beagle Gulf and into the Timor Sea.  The increased convection and organization prompted the Australian Bureau of Meteorology to name the system Tropical Cyclone Blanche.

Although the circulation of Tropical Cyclone Blanche became better organized today, it is still somewhat asymmetrical.  Many of the stronger thunderstorms are occurring in a band south and west of the center or circulation.  Bands north and east of the center contain mainly lower clouds and showers.  An upper level ridge to the east of Blanche is producing northerly winds which are blowing toward the top of the tropical cyclone.  The vertical wind shear appears to have increased during recent hours and the upper level divergence to the east of the center has been reduced.  Part of the lower level circulation appears to becoming exposed on the most recent visible satellite images.

Tropical Cyclone Blanche will be moving through an environment that contains both positive and negative factors.  Blanche will move over water where the Sea Surface Temperature is near 29°C.  So, there is sufficient energy in the upper ocean to support intensification.  However, the upper level ridge to the east of Blanche is producing moderate vertical wind shear, which appears to have stalled intensification for now.  If the wind shear remains moderate, then Blanche will not strengthen.  If the wind shear increases, it could blow the upper portion of the circulation away from the lower part and the tropical cyclone would weaken.  On the other hand if the wind shear decreases, then Tropical Cyclone Blanche could intensify a little more.  There is a great deal of uncertainty about the future intensity of Blanche.

Blanche is moving around the northwestern portion of a subtropical ridge, which is steering the tropical cyclone toward the southwest.  This general motion is expected to continue.  On its anticipated track Tropical Cyclone Blanche will move across the Timor Sea and make landfall on the coast of Western Australia between Wyndham and Kalumburu in 24 to 36 hours.  Tropical Cyclone Blanche could bring some gusty winds, but the primary risk will be locally heavy rainfall and the potential for flooding.

Tropical Cyclone Enawo Forms North of La Reunion

Tropical Cyclone Enawo formed north of La Reunion on Friday.  At 4:00 p.m. EST on Friday the center of Tropical Cyclone Enawo was located at latitude 13.2°S and longitude 56.2°E which put it about 520 miles (835 km) north of St. Denis, La Reunion.  Enawo was moving toward the southwest at 4 m.p.h.  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (105 km/h).  The minimum surface pressure was 994 mb.

An area of low pressure organized slowly over the southwest Indian Ocean during the past few days.  Bands of thunderstorms formed west of the center of circulation and some of the bands began to wrap closer to the center on Friday.  The low pressure system exhibited the characteristic structure of a developing tropical cyclone and it was designated Tropical Cyclone Enawo.  Although there are more thunderstorms near the center of circulation, the distribution of the storms is still asymmetrical.  There are many more thunderstorms in the western half of the circulation.  The asymmetry probably indicates that some vertical wind shear is slowing the organization of the circulation.

Tropical Cyclone Enawo will be moving through an environment favorable for intensification during the next several days.  It will be moving over water where the Sea Surface Temperature is near 30°C.  Enawo is northwest of an upper level ridge which is generating easterly winds that are blowing toward the top of the circulation.  The upper level ridge could be the source of the vertical wind shear that is slowing the intensification of the tropical cyclone.  The upper level wind shear could decrease during the weekend and Tropical Cyclone Enawo is likely to intensify into the equivalent of a hurricane/typhoon.  Once an inner core become well established at the center of circulation, a period of rapid intensification may be possible.

A subtropical ridge located southeast of Enawo is steering the tropical cyclone toward the southwest.  Guidance from the numerical models is divergent about the future strength of the ridge.  Some of the models, like the Global Forecasting System,  are predicting a weaker ridge and turn Tropical Cyclone Enawo more toward the south.  Other models, such as the European Center for Medium Range Forecasting System model, strengthen the subtropical ridge and steer Tropical Cyclone Enawo west toward northeast Madagascar.  Given the uncertainty in both the track and intensity forecasts, interests in the southwest Indian Ocean should monitor Tropical Cyclone Enawo closely.