Monthly Archives: January 2016

Tropical Cyclone Stan Brings Wind and Rain to Western Australia

Tropical Cyclone Stan brought wind and rain to the coast of Western Australia as it made landfall on Saturday.  At 2:00 p.m. EDT on Saturday the center of Tropical Cyclone Stan was located at latitude 20.0°S and longitude 119.9°E which put it about 22 miles (35 km) east-northeast of Pardoo Station, Australia.  Stan was moving toward the south-southeast at 13 m.p.h. (20 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were wind gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 977 mb.

The center of Tropical Cyclone Stan made landfall just east of Pardoo Station.  The circulation of Stan is relatively small and tropical storm force winds only extend about 100 miles from the center.  Most of the heavy rain is occurring west of the center of circulation between Pardoo and Port Hedland.

Tropical Cyclone Stan is moving around the western end of a subtropical ridge.  A trough in the middle levels of the atmosphere is west of Stan and it is helping to steer the tropical cyclone toward the southeast.  That general motion is expected to continue during the next 24 hours.  On its anticipated track Tropical Cyclone Stan will move farther inland over Western Australia.  It could pass near Yarrie in a few hours.

Tropical Cyclone Stan will continue to weaken steadily as it moves farther inland.  It could cause localized wind damage.  Stan could also produce locally heavy rain in isolated locations.

Tropical Cyclone Stan Intensifying As It Nears Western Australia

Tropical Cyclone Stan intensified on Friday as it moved closer to the coast of Western Australia.  At 4:00 p.m. EDT on Friday the center of Tropical Cyclone Stan was located near latitude 18.6°N and longitude 118.9°E which put it about 120 miles (195 km) north of Port Hedland, Australia.  Stan was moving toward the east-southeast at 6 m.p.h. (10 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 982 mb.

The circulation of Tropical Cyclone Stan is much more well organized than it was 24 hours ago.  A primary rainband has wrapped about two thirds of the way around a distinct center of circulation.  There are many more thunderstorms in the core of the circulation and the structure is more symmetrical.  Thunderstorms in the core of Tropical Cyclone Stan are beginning to generate more upper level divergence which is pumping out mass in all directions.

The environment surrounding Tropical Cyclone Stan is now more favorable for intensification.  Stan has moved closer to the center of an upper level ridge that is located east of the tropical cyclone.  As a result, the upper level winds are not as strong and there is less vertical wind shear.  Since Tropical Cyclone Stan is over water where the Sea Surface Temperature is near 29°C, the reduced wind shear allowed it to intensify significantly today.  The environment will be favorable for intensification until Tropical Cyclone Stan makes landfall, and it could become the equivalent of a hurricane within 12 hours.  A period of rapid intensification may be possible.

As Tropical Cyclone Stan moved into an area where the easterly winds in the middle and upper levels were not as strong, it jogged eastward on Friday.  Stan is moving around the western end of a subtropical ridge and it is expected to begin to move more toward the southeast during the next 12 to 24 hours.  The eastward jog today also moved the most likely landfall location to the east.  On its anticipated track Tropical Cyclone Stan is expected to make landfall on the coast of Western Australia in 12 to 24 hours.  The highest probability of landfall is between Broome and Port Hedland near Pardoo Station.

Tropical Cyclone Stan will likely be the equivalent of a hurricane when it makes landfall.  It will be capable of causing wind damage.  Stan will also bring locally heavy rain and a chance for flash floods.  Tropical Cyclone Stan could generate a significant storm surge along the coast near where the center makes landfall.

Tropical Cyclone Stan Heading for Western Australia

A tropical low intensified into Tropical Cyclone Stan on Thursday and it is moving toward Western Australia.  At 10:00 p.m. EST on Thursday the center of Tropical Cyclone Stan was located at latitude 17.7°N and longitude 117.8°E which put it about 190 miles (305 km) north-northwest of Port Hedland, Australia.  Stan was moving toward the south-southeast at 7 m.p.h. (11 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 995 mb.

Tropical Cyclone Stan is not particularly well organized.  A primary rainband curves around the western side of the circulation, but there are not many thunderstorms in the eastern half of the cyclone.  Upper level divergence is occurring to the west of the center, but not to the east of the center.

The environment is marginally favorable for further intensification.  Tropical Cyclone Stan is over water where the Sea Surface Temperature is near 29°C.  However, an upper level ridge east of Stan is generating easterly winds over the top of the tropical cyclone.  The resulting vertical wind shear is inhibiting upper level divergence to the east of Stan.  The tropical cyclone is extracting enough energy from the ocean to intensify but the vertical wind shear is slowing the rate of intensification.  Tropical Cyclone Stan is expected to continue to intensify until it makes landfall.

Tropical Cyclone Stan is moving around the western end of a subtropical ridge which is steering it toward the south-southeast.  The south-southeast motion is expected to continue for another 24 to 36 hours.  On its anticipated track Tropical Cyclone Stan will make landfall on the coast of Western Australia near Port Hedland in about 24 hours.

Tropical Cyclone Stan could be near hurricane intensity when it makes landfall.  It will be capable of causing some wind damage.  Stan could also produce locally heavy rain and flooding.  It will also cause some storm surge near where the center makes landfall.

Tropical Cyclone Organizing Northwest of Australia

A tropical cyclone is organizing northwest of Australia and the Australian Bureau of Meteorology has officially designated it as a tropical low.  At 10:00 p.m. EST on Wednesday the center of the tropical low was located at latitude 15.4°S and longitude 117.7°E which put it about 345 miles (555 km) north of Port Hedland, Australia.  The tropical low was moving toward the south at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1001 mb.

The circulation around the tropical low is still in an organizational phase and there is no well defined center of circulation.  Scattered spiral bands of thunderstorms are beginning to form and rotate around a broad center of circulation.  Much of the convection is still relatively shallow and taller thunderstorms are just beginning to form.  Some upper level divergence is beginning to occur to the west of the tropical low.

The environment is favorable for intensification.  The tropical low is over water where the Sea Surface Temperature is near 30°C.  An upper level ridge east of the tropical low is generating some easterly winds over the system, but the vertical wind shear is probably not strong enough to prevent intensification.  After more thunderstorms consolidate around a center of circulation and the organization of the tropical low improves, intensification is likely.

A subtropical ridge east of the tropical low is steering the low toward the south and that general motion is expected to continue for the next several days.  On its anticipated track, the tropical low could make landfall somewhere along the coast of Western Australia between Broome and Mardie on Friday.  The highest probability is currently for a landfall near Port Hedland in about 48 hours.  However, uncertainty exists about the future track because the tropical low is still organizing and a well defined center of circulation does not yet exist.

The tropical low is likely to bring strong winds, locally heavy rain and some storm surge to parts of the coast of Western Australia.

Tropical Cyclone Victor Moves Toward Tonga

Tropical Cyclone Victor moved slowly westward toward Tonga as it passed south of Niue on Wednesday.  At 4:00 p.m. EST on Wednesday the center of Tropical Cyclone Victor was located at latitude 21.5°S and longitude 169.8°W which put it about 155 miles (250 km) south of Niue and about 370 miles (595 km) east of Tonga.  Victor was moving toward the west at 4 m.p.h. (6 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were wind gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 977 mb.

Tropical Cyclone Victor still looks like the equivalent of a hurricane on satellite images.  It has a well formed eye which is surrounded by a ring of thunderstorms.  The thunderstorms near the center of Victor are generating a large area of upper level divergence.  Convection outside of the core of Victor is somewhat asymmetrical.  Most of the stronger thunderstorms are located in bands south and east of the center of circulation.  There are few tall thunderstorms in the northwestern part of Victor.

Tropical Cyclone Victor continues to be in an environment that is favorable for intensification.  Victor is moving over water where the Sea Surface Temperature is near 27°C.  The upper level winds near Victor are light and there is no appreciable vertical wind shear.  Tropical Cyclone Victor has the potential to intensify during the next 24 hours.

A subtropical ridge south of Victor is steering the tropical cyclone slowly toward the west.  The ridge is expected to continue to steer Victor toward the west, but at a faster speed, during the next day or two.  On its anticipated track Tropical Cyclone Victor could be approaching Tonga in about 36 hours.

Tropical Cyclone Victor passed far enough south of Niue that the stronger winds and heavy rain did not affect the island.  Large waves and surf may have affected some of the coastal areas.  Tropical Cyclone Victor could bring wind and rain to Tonga in two or three days.

Tropical Cyclone Victor Intensifies East of Niue

Tropical Cyclone Victor intensified on Monday and it is now the equivalent of a Category 2 hurricane on the Saffir-Simpson Scale.  At 4:00 p.m. EST on Monday the center of Tropical Cyclone  Victor was located at latitude 20.2°S and longitude 166.3°W which put it about 175 miles (280 km) east-southeast of Niue.  Victor was moving toward the south-southwest at 5 m.p.h. (8 km/h).  The maximum sustained wind speed was 105 m.p.h. (170 km/h) and there were wind gusts to 125 m.p.h. (205 km/h).  The minimum surface pressure was 956 mb.

Tropical Cyclone Victor has an unusual structure.  It has a very large eye, which is about one degree of longitude across.  The eye is surrounded by a narrow eyewall of strong thunderstorms and a couple of thin, primary rainbands.  Winds to tropical storm force extend out about 200 miles (320 km) from the center of circulation.  The thunderstorms in the eyewall are generating strong upper level divergence which is pumping out mass.  The eye has appeared to contract a bit on recent satellite imagery, which could be a sign of further intensification.

Tropical Cyclone Victor is an environment that is favorable for intensification.  It is moving over water where the Sea Surface Temperature (SST) is near 27°C.  An upper level ridge located northeast of Victor is producing some light northwesterly winds over the top of the tropical cyclone.  However, the vertical wind shear is minimal and it is not inhibiting intensification at this time.  Victor could continue to intensify on Tuesday.  Later this week Tropical Cyclone Victor will move into an environment with cooler SSTs and more wind shear.  Victor will start to weakening when it enters that environment.

The ridge northeast of Victor is getting stronger and it is forcing the tropical cyclone to move toward the west-southwest.  That general motion is expected to continue for the next several days.  On its anticipated track the core of Tropical Cyclone Victor with the strongest winds will pass south of Niue during the next 48 hours.  However, Tropical Cyclone Victor could bring a period of strong winds and rain to Niue as it moves south of the islands.  The large wind field around Victor could also generate significant waves and surges.  Tropical Cyclone Victor could be approaching Tonga later this week.

Tropical Storm Alex Brings Wind and Rain to the Azores

Tropical Storm Alex weakened to just below hurricane intensity as it moved across the Azores on Friday morning.  At 10:00 a.m. EST the center of Hurricane Alex was located at latitude 39.3°N and longitude 27.0°W which put it about 35 miles north of Terceira in the Azores.  Alex was moving toward the north at 28 m.p.h. (44 km/h).  The maximum sustained wind speed was 70 m.p.h. (115 km/h) and there were wind gusts to 85 m.p.h. (135 km/h).  The minimum surface pressure was 986 mb.

It appears that the center of Tropical Storm Alex made landfall on the island of Terceira.  Weather stations on Santa Maria and Sao Miguel have measured tropical storm force winds.  However, it seems like the core of Tropical Storm Alex which contains the strongest winds remained over water.  Higher wind speeds most likely occurred on the windward sides of mountains in the Azores.

In anticipation of the movement of Tropical Storm Alex away from the islands all Hurricane Warnings and Tropical Storm Warnings for the Azores have been discontinued.

Tropical Storm Alex is over water where the Sea Surface Temperature is near 16°C.  It will move over even cooler water and Alex will soon be unable to extract enough energy from the ocean to sustain the structure of a tropical cyclone.  The structure of Alex will gradually change to the structure of a cold core extratropical cyclone during the next several days.  It is likely to maintain much of its intensity as it moves through the extratropical transition.

An upper level trough is steering Tropical Storm Alex toward the north-northwest and a general northwesterly motion is expected to continue for the next two or three days.  Tropical Storm Alex could end up south of Greenland over the weekend as a strong extratropical cyclone.

Subtropical Storm Alex Transitions to Hurricane, Threatens the Azores

The structure of Subtropical Storm Alex evolved into the structure associated with a tropical cyclone and the National Hurricane Center reclassified it as Hurricane Alex on Thursday morning.  At 10:00 a.m. EST on Thursday the center of Hurricane Alex was located at latitude 31.5°N and longitude 28.4°W which put it about 490 miles (790 km) south of Faial in the Central Azores.  Alex was moving toward the north at 20 m.p.h. (32 km/h).  The maximum sustained wind speed was 85 m.p.h. (140 km/h) and there were wind gusts to 105 m.p.h. (170 km/h).  The minimum surface pressure was 981 mb.

A Hurricane Warning has been issued for Faial, Pico, Sao Jorge, Graciosa, and Terceira in the Central Azores.  A Tropical Storm Warning has been issued for Sao Miguel and Santa Maria in the Eastern Azores.

Alex has developed the structure associated with a small hurricane.  An eye is clearly visible on satellite imagery.  A ring of thunderstorms surrounds the eye and there are spiral bands rotating around the core of the circulation.  Latent energy released by convection around the core of Hurricane Alex generated a warm core in the middle and upper troposphere.  That convection is also generating upper level divergence which is pumping out mass, especially to the north and east of the center.

Hurricane Alex is over water where the Sea Surface Temperatures (SSTs) are near 20.5°C.  Those SSTs are usually considered to be too cold to supply enough energy to promote the development of a hurricane.  However, it is January and the temperatures in the middle and upper troposphere are also cold.  So, there is clearly enough instability to generate convection and create a hurricane.  The thunderstorms are in Alex are not as tall as they would be if the SSTs are warmer.  The shorter thunderstorms do not extend into the stronger winds in the upper troposphere and Hurricane Alex is not experiencing as much vertical wind shear as might be expected.   The combination of more instability and less vertical wind shear allowed Alex to transition from a subtropical storm to a hurricane.

The upper level divergence could allow Alex to intensify a little more during the next 12 hours.  Hurricane Alex will move over SSTs that are even colder and at some point the structure of Alex will change again.  It will develop fronts and transition into an extratropical cyclone.

Alex is being steered northward by an upper level trough to its west and that general motion is expected to continue for the next several days.  On its anticipated track Hurricane Alex will move over portions of the Azores on Friday.

The Hurricane Intensity Index (HII) for Alex is 12.7.  The Hurricane Size Index is (HSI) 7.0.  The Hurricane Wind Intensity Size Index (HWISI) is 19.7.  Those indices suggest that Hurricane Alex is capable of causing localized minor damage with isolated areas of serious damage.

Alex is the first Atlantic hurricane to form during the month of January since 1938.  Alex is the first tropical cyclone be a hurricane in January since Hurricane Alice in 1955.

Hurricane Pali Weakens As It Nears the Equator

Hurricane Pali weakened quickly on Wednesday as it moved closer to the Equator and it is now classified as a tropical storm.  At 10:00 p.m. EST on Wednesday the center of Tropical Storm Pali was located at latitude 2.7°N and longitude 172.2°W which put it about 330 miles (530 km) east-northeast of Howland Island.  Pali was moving toward the south-southwest at 9 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 993 mb.

As Hurricane Pali moved closer to the Equator, it moved into an area of strong vertical wind shear and weakened.  A large area of thunderstorms east-northeast of Samoa could be consolidating into a new tropical cyclone.  That area of thunderstorms is generating a lot of upper level divergence which is spreading across the Equator as strong upper level winds from the south.  Those upper level winds created strong vertical wind shear over Pali as the hurricane moved south on Wednesday.  The wind shear pushed the upper portion of Tropical Storm Pali toward the north and disrupted the vertical integrity of Pali’s circulation.  The lack of vertical integrity resulted in a significant decrease in the surface wind speed on Wednesday.

The environment around Tropical Storm Pali will be unfavorable for intensification for the next several days.  The vertical wind shear will continue and it could increase if a tropical cyclone develops east of Samoa.  Tropical Storm Pali is expected to continue to weaken on Thursday.  However, if the surface circulation remains intact for another 48 hours, the wind shear could decrease during the weekend.  The Sea Surface Temperature is near 30°C and so there is sufficient energy to support intensification, if the upper level winds decrease.  If there is still a surface circulation on Saturday, then it could begin to reorganize and get stronger.  Alternatively, if the wind shear gets stronger, Tropical Storm Pali could dissipate over the weekend.

A subtropical ridge to the northwest of Pali is steering the tropical storm toward the south.  As Pali weakens, the low level circulation will be steered more by winds closer to the surface.  Those winds are blowing from the east and Tropical Storm Pali or its remnants are expected to move toward the west during the next few days.

Subtropical Storm Alex Develops over East Atlantic

A low pressure system over the eastern Atlantic Ocean has been classified as Subtropical Storm Alex by the National Hurricane Center.  At 4:00 p.m. EST on Wednesday the center of Subtropical Storm Alex was located at latitude 27.1°N and longitude 30.8°W which put it about 785 miles (1260 km) south-southwest of the Azores.  Alex was moving toward the northeast at 14 m.p.h. (23 km/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 990 mb.

Subtropical Storm Alex evolved out of an extratropical cyclone that formed off the southeastern coast of the U.S. late last week.  The extratropical cyclone cycled through the typical stages exhibited by low pressure systems in the middle latitudes as it moved eastward across the central Atlantic Ocean.  It eventually became an occluded extratropical cyclone over that region.  The low pressure system moved south on Tuesday, which placed it over slightly warmer Sea Surface Temperatures (SSTs).  As it began to extract more energy from the warmer ocean, the fronts attached to the low pressure system began to dissipate.  The low began to take on a more circular shape and convection began to intensify around the center of circulation.  A more circular shape with no fronts and taller clouds prompted the National Hurricane Center to classify the low as a subtropical storm.

A subtropical storm is a hybrid low with some characteristics of a tropical cyclone (circular shape and no fronts) and some characteristics of an extratropical cyclone (cooler air aloft).  Subtropical Storm Alex has a well organized low level circulation.  There is a clear area in the center that looks a little like the eye of a hurricane.  The center is surrounded by a ring of taller clouds.  Spirals bands of clouds are rotating around the core of the circulation.  However, the vertical structure is different from a tropical cyclone.  Subtropical Storm Alex is under an upper level trough and the upper level divergence is limited.  Also, the clouds in Alex are not growing as tall as the clouds in a tropical cyclone.

The environment around Subtropical Storm Alex would normally be considered to be unfavorable for intensification of a tropical cyclone.  The SSTs are near 23.5°C.  However, since Alex is near the center of an upper level trough, there is not much vertical wind shear.  So, there could be a chance for some intensification during the next 24 hours.  Subtropical Storm Alex will move over cooler SSTs and it is likely to make a transition back to an extratropical cyclone in two or three days.

The upper level trough is steering Alex toward the northeast and a general northward motion is expected to continue for the next several days.  On its anticipated track Subtropical Storm Alex could approach the Azores in about 36 hours.  It could bring strong winds and locally heavy rain when it moves over the Azores.

Subtropical Storm Alex is the first tropical or subtropical cyclone to form over the North Atlantic Ocean in January since 1978.  It is only the fourth tropical or subtropical cyclone on record to form over the Atlantic Ocean in January since 1851.