Monthly Archives: March 2015

Tropical Cyclone Nathan Expected to Intensify and Move Toward Northern Queensland

After making a long slow clockwise loop, Tropical Cyclone Nathan is expected to intensify and move toward Northern Queensland.  At 10:00 p.m. EDT on Tuesday the center of Tropical Cyclone Nathan was located at latitude 15.2°S and longitude 149.2°E which put it about 270 miles east of Cooktown, about 260 miles east-northeast of Cairns and about 330 miles northeast of Townsville, Australia.  Nathan was moving toward the west-southwest at 3 m.p.h.  The maximum sustained wind speed was 60 m.p.h. and there were wind gusts to 80 m.p.h.  The minimum surface pressure was 983 mb.

Wind shear had been inhibiting the re-organization of the circulation around Tropical Cyclone Nathan.  However, it has moved into a much more favorable environment and the circulation has consolidated.  Satellite imagery indicates that Nathan now looks like a classical tropical cyclone with an area of thunderstorms at its center and spiral bands rotating around the core.  Nathan is over warm Sea Surface Temperatures and in an area where the upper level winds are light.  So, further intensification is likely and rapid intensification is possible.

The steering currents around Nathan have been weak.  However, a subtropical ridge is expected to build southwest of the tropical cyclone and steer it westward toward northern Queensland.  The projected track would bring the center of Nathan to the coast near Cooktown in about 36 to 48 hours.   Nathan is expected to intensify during that time and it could be a strong tropical cyclone when it makes landfall.  It has the potential to bring strong winds and a significant storm surge when it reaches the coast.  It could also bring locally heavy rain and possibly flooding as the circulation moves inland over northeastern Queensland.

Wind Shear Still Affecting Tropical Storm Bavi

Strong southerly winds in the upper levels are creating vertical wind shear over Tropical Storm Bavi.  At 11:00 p.m. EDT on Sunday the center of Tropical Storm Bavi was located at latitude 13.4°N and longitude 140.7°W which put it about 250 miles west of Guam and about 1070 miles east of the Philippines.  Bavi was moving toward the west at 22 m.p.h.  The maximum sustained wind speed was 45 m.p.h. and there were wind gusts to 55 m.p.h.  The minimum surface pressure was 993 mb.

A strong upper level ridge east of Bavi is generating brisk southerly winds over the top of the circulation.  Those winds are causing most of the thunderstorms to occur north of the center of circulation.  The structure of the cyclone also appears to be tilted toward the north.  The poor organization of the circulation is preventing it from intensifying.  If the upper level winds do not decrease, it will be difficult for Bavi to organize further.

A subtropical ridge to the north of Bavi is steering it toward the west.  This general motion is expected to continue for the next few days.  The projected track would bring Bavi or its remnants near the Philippines in a few days.

Tropical Cyclone Nathan Organizing Slowly East of Queensland

The structure of Tropical Cyclone Nathan improved on Sunday and it intensified slowly.  At 11:00 p.m. EDT on Sunday the center of Tropical Cyclone Nathan was located at latitude 13.9°N and longitude 149.8° which put it about 300 miles east-northeast of Cooktown, about 420 miles north-northeast of Townsville, Australia and about 250 miles north of Willis Island.  Nathan was moving toward the east-southeast at 3 m.p.h.  The maximum sustained wind speed was 65 m.p.h. and there were gusts to 80 m.p.h.  The minimum surface pressure was 984 mb.

Spiral bands of thunderstorms wrapped around the center of circulation and the structure of Nathan looks more well organized.  It is over warm Sea Surface Temperatures and the upper level winds are not too strong.  As a result, Nathan appears to be developing stronger upper level outflow.  The upper level outflow is pumping out mass, which is allowing the pressure to decrease and the wind speed to increase.  The environment around Nathan could support further intensification during the next 48 hours.

A ridge located northeast of Nathan is steering it slowly toward the south and that motion is likely to continue over the short term.  The winds steering the tropical cyclone could weaken in 24 to 48 hours, which could result in a period of little movement.  Later in the week a second ridge is expected to build northwest of Nathan and start to steer it westward which would move it closer to the east coast of Australia.   The projected track could bring Nathan very close to Willis Island in three or four days.

Tropical Storm Bavi Nearing Guam

Tropical Storm Bavi is moving rapidly toward Guam.  At 11:00 p.m. EDT on Saturday the center of Tropical Storm Bavi was located at latitude 13.8°N and longitude 148.7°E which put it about 100 miles east-northeast of Guam.  Bavi was moving toward the west at 18 m.p.h.  The maximum sustained wind speed was 50 m.p.h. and there were gusts to 65 m.p.h.  The minimum surface pressure was 989 mb.

Bavi is moving over water where the Sea Surface Temperatures are around 27.5°C.  So, there is sufficient energy to support intensification.  Moderate easterly winds in the upper levels are generating vertical wind shear over the circulation.  Most of the thunderstorms have been located in the western half of the circulation.  However, recent satellite imagery indicates that there may be more thunderstorms forming near the core of the circulation.  The rapid movement of the storm and the wind shear are likely to limit potential intensification.

A subtropical ridge to the north of Bavi is steering it rapidly to the west and that motion is expected to continue.  Bavi will move  near Guam within a few hours and the core of the circulation could pass near Rota, Tinian and Saipan.  It is likely to bring gusty winds and locally heavy rains as it passes.  The subtropical ridge is expected to steer Bavi or its remnants toward the Philippines during the next few days.

Tropical Cyclone Pam Weakening North of New Zealand

Tropical Cyclone Pam is on a weakening trend as it moves north of New Zealand.  At 11:00 p.m. EDT on Saturday the center of Tropical Cyclone Pam was located at latitude 29.3°S and longitude 175.0°E which put it about 500 miles north of Auckland, New Zealand.  Pam was moving toward the south-southeast at 33 m.p.h.  The maximum sustained wind speed was 115 m.p.h. and there were gusts to 135 m.p.h.  The minimum surface pressure was 948 mb.

Pam has moved over water where the Sea Surface Temperature is 25°C and it is no longer able to extract sufficient energy from the ocean to maintain its intensity.  Stronger winds in the upper levels are increasing the vertical wind shear over the circulation and the weakening trend should continue.  The steering flow should carry Pam east of New Zealand and farther out into the South Pacific Ocean.

Tropical Cyclone Nathan Moving Away From Queensland

Tropical Cyclone Nathan started moving eastward away from Queensland on Saturday.  At 10:00 p.m. EDT on Saturday the center of Tropical Cyclone Nathan was located at latitude 13.4°S and longitude 148.5°E which put it about 400 miles northeast of Townsville, Australia.  Nathan was moving toward the east at 10 m.p.h.  The maximum sustained wind speed was 50 m.p.h. and there were wind gusts to 65 m.p.h.  The minimum surface pressure was 989 mb.

The circulation around Nathan showed signs of increasing organization with a long spiral band beginning to wrap around the center.  It is possible that the long period of time Nathan was stationary caused it to upwell cooler water.  As it moves eastward, the center of circulation is moving back over warmer Sea Surface Temperatures which are supplying more energy to the system.  Nathan is in an area where the upper level winds are relatively light and it has the potential to intensify during the next day or two.

A ridge located north of Nathan is steering it toward the east.  The steering currents are expected to weaken in 24 to 48 hours and Nathan could stall again.  Numerical guidance is providing conflicting indications about the longer term track.  Some guidance turns the tropical cyclone back to the southwest, while other guidance pushes the system farther to the east.

Intense Tropical Cyclone Pam Moving Over Southeastern Vanuatu

Very intense Tropical Cyclone Pam has been moving over some of the southeastern islands of Vanuatu  during Friday.  At 5:00 p.m. EDT on Friday the center of Tropical Cyclone Pam was located at latitude 19.3°S and longitude 169.1°E which put ti about 10 miles northwest of Tanna, Vanuatu and about 120 miles northeast of Noumea, New Caledonia.  Pam was moving toward the south at 12 m.p.h.  The maximum sustained wind speed was 155 m.p.h. and it was estimated that there were wind gusts to 190 m.p.h.  The minimum surface pressure was 922 mb.

The center of Pam moved very close to the islands of Efate, Erromango and Tanna.  Given the size and intensity of the circulation, it is likely that it caused significant damage on those islands.  Pam may have reached its peak intensity and there are some indications that it could be undergoing an eyewall replacement cycle.  Some fluctuation or decrease in intensity is likely during the next 24 hours.

The center of Pam is projected to pass east of New Caledonia.  However, it may get close enough to cause significant damage, especially to the islands of Ouvea, Lifou and Mare, which will be closer to the center of circulation.  Pam should begin to weaken more quickly as it moves farther south in the general direction of New Zealand.

 

Tropical Storm Bavi Moving Toward Guam

Tropical Storm Bavi continued to move rapidly toward the west-northwest toward Guam on Friday.  At 5:00 p.m. EDT on Friday the center of Tropical Storm Bavi was located at latitude 10.7°N and longitude 157.6°E which put it about 880 miles east-southeast of Guam.  Bavi was moving toward the west-northwest at 17 m.p.h.  The maximum sustained wind speed was 45 m.p.h. and there were gusts to 60 m.p.h.  The minimum surface pressure was 989 mb.

Strong easterly winds in the upper levels are creating vertical wind shear and are inhibiting intensification of Bavi.  The wind shear is also causing most of the thunderstorms to be located on the western side of the circulation.  Thus, Bavi is not well organized at the current time.  However, Bavi is moving over warm Sea Surface Temperatures and it could strengthen slowly as it moves farther west, if the wind shear decreases.

A strong subtropical ridge to the north of Bavi is steering it rapidly westward.  Bavi could be in the vicinity of Guam in about 48 hours.  The ridge is expected to continue to steer Bavi westward after it moves past Guam and it could approach the Philippines in a few days.

Tropical Cyclone Olwyn Near Carnarvon, Australia

The center of Tropical Cyclone Olwyn has been moving roughly parallel to the coast of Western Australia and it is near Carnarvon.  At 11:00 p.m. EDT on Thursday the center of Tropical Cyclone Olwyn was located at latitude 24.6°S and longitude 113.4°E which put it about 20 miles northwest of Carnarvon and about 100 miles north of Denham, Australia.  Olwyn was moving toward the south-southwest at 15 m.p.h.  The maximum sustained wind speed was 100 m.p.h. and there were gusts to 120 m.p.h.  The minimum surface pressure was 959 mb.  Earlier on Thursday the airport at Learmonth measured sustained winds to 84 m.p.h. and a pressure of 970 mb when the center of Olwyn passed just to its west.

Olwyn is being steered southward by a subtropical ridge to its east.  The projected path takes the center of circulation inland and then moves it parallel to the coast.  When Olwyn moves inland it will start to weaken.  However, if there is a slight deviation of the track to the west which keeps the center of circulation over water for a longer period of time, it would keep the circulation stronger.  The latter possibility would extend the risk for wind damage farther south along the coast.  In either case, the clockwise rotation around the center and the shape of the coast could produce a significant storm surge in Shark Bay.  There is also a potential for locally heavy rainfall and flooding near the coast.

Pam Reaches Equivalent of Category 5 Hurricane

Tropical Cyclone Pam continued to intensify on Thursday and it has attained an intensity equivalent to a Category 5 hurricane on the Saffir-Simpson Scale.  At 5:00 p.m. the center of Tropical Cyclone Pam was located at latitude 15.0°S and longitude 169.6°E which put it about 100 miles east of Maewo, Vanuatu and about 560 miles northwest of Fiji.  Pam was moving toward the west-southwest at 10 m.p.h.  The maximum sustained wind speed was 160 m.p.h. and it was estimated that there could be wind gusts to 200 m.p.h.  The minimum surface pressure was 918 mb.

Pam is in an almost ideal environment for a tropical cyclone.  The Sea Surface Temperatures are warm and the upper level winds are very light.  It has a well developed circulation with a tight inner core.  Upper level divergence is pumping out mass in all directions.  Some further intensification is possible during the shorter term.  Eventually, when Pam moves farther south in a couple of days, it will move over cooler Sea Surface Temperatures and into a region where the upper level winds are stronger.  At that time it should start a steady weakening trend.  In the interim eyewall replacement cycles could produce fluctuations in intensity, but Pam is likely to be a big strong tropical cyclone for several more days.

An upper level ridge to the east of Pam is steering it generally toward the south.  It has moved a little west of due south today and that has brought the western part of the circulation closer to Vanuatu.  Any further westward movement could bring strong winds very close to Maewo, Pentecote, Ambrym, Epi, Efate and numerous smaller islands in southeastern Vanuatu.  Pam is a large, strong tropical cyclone and it is capable of causing serious damage on any island it crosses.