Tag Archives: the Azores

Tropical Storm Maria Brings Gusty Winds, Big Waves to Outer Banks

Tropical Storm Maria brought gusty winds and big waves to the Outer Banks of North Carolina on Tuesday night.  At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Maria was located at latitude 34.9°N and longitude 72.9°W which put it about 150 miles (240 km) east of Cape Hatteras, North Carolina.  Maria was moving toward the north at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 70 m.p.h. (110 km/h) and there were wind gusts to 85 m.p.h. (135 km/h).  The minimum surface pressure was 975 mb.

A Tropical Storm Warning is in effect for the portion of the coast from Bogue Inlet, North Carolina to the North Carolina/Virginia border including Albemarle and Pamlico Sounds.

Most of the showers and thunderstorms are occurring in the eastern half of the circulation of Tropical Storm Maria.  The strongest winds are also occurring in the eastern half of Maria.  Winds to tropical storm force extend out about 230 miles (370 km) east of the center of circulation and about 185 miles (295 km) to the west of the center.  A NOAA buoy (41025) at Diamond Shoals was reporting sustained winds to near tropical storm force.  The large size and slow movement of Tropical Storm Maria were causing large waves that were reaching the Outer Banks of North Carolina.

Tropical Storm Maria is moving around the western end of a subtropical high pressure system over the Atlantic Ocean.  The high will steer Maria slowly toward the north on Wednesday.  An upper level trough approaching the eastern U.S. will start to steer Maria toward the east on Thursday.  The upper level trough will push Tropical Storm Maria away from the U.S. on Friday.  When Maria moves over cooler water it will make a transition to an extratropical cyclone.

Elsewhere over the Atlantic Ocean, small Hurricane Lee neared major hurricane intensity.  At 11:00 p.m. EDT on Tuesday the center of Hurricane Lee was located at latitude 30.0°N and longitude 55.5°W which put it about 570 miles (920 km) east-southeast of Bermuda.  Lee was moving toward the west at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 110 m.p.h. (175 km/h) and there were wind gusts to 130 m.p.h. (210 km/h).  The minimum surface pressure was 971 mb.

Hurricane Lee has a small, well organized circulation.  There is a small eye at the center of circulation.  The eye is surrounded by a ring of strong thunderstorms.  Several bands of showers and thunderstorms are revolving close to the core of Hurricane Lee.  Winds to hurricane force only extend out about 25 miles (40 km) from the center of circulation.  Winds to tropical storm force extend out about 60 miles (95 km) from the center.

Hurricane Lee could intensify into a major hurricane on Wednesday.  Lee will move over water where the Sea Surface Temperature is near 28°C.  The upper level winds will be weak on Wednesday and there will be little vertical wind shear.  Wind shear will increase later in the week when the upper level trough approaching the eastern U.S. gets closer to Hurricane Lee.

TD 01 Intensifies Into Rare April Tropical Storm Arlene

Tropical Depression 01 intensified into Tropical Storm Arlene on Thursday afternoon.  Tropical storms rarely form over the Atlantic Ocean in April and Arlene is only the second storm known to do so during the satellite era.  Of course, it would have been much harder to detect tropical storms like Arlene prior to the use of geostationary satellites for meteorological monitoring.  At 5:00 p.m. EDT on Thursday the center of Tropical Storm Arlene was located at latitude 37.7°N and longitude 42.0°W which put it about 815 miles (1315 km) west of the Azores.  Tropical Storm Arlene was moving toward the west-northwest at 25 m.p.h. (41 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 936 mb.

A circular ring of showers and thunderstorms developed around the center of circulation of Subtropical Depression 01.  Additional narrow rainbands organized around the core of the circulation and the convection assumed a more circularly symmetrical shape.  In addition data from satellites indicated that a weak warm core had formed at the top of the circulation.  A more circular shape and a warm core are characteristics of a tropical cyclone and the National Hurricane Center changed the classification of Subtropical Depression 01 to Tropical Depression 01 in the 11:00 a.m. EDT advisory on Thursday.  Showers and thunderstorms continued to develop around the center of circulation and Tropical Depression 01 was upgraded to Tropical Storm Arlene in the 5:00 p.m. EDT advisory on Thursday.

Tropical Storm Arlene is in an environment that would not normally be considered favorable for a purely tropical weather system.  It is moving over water where the Sea Surface Temperature (SST) is near 19°C.  However, an upper low just to the west of Arlene contains colder air.  Colder air in the upper levels is providing sufficient instability to generate showers and thunderstorms even though the SST is relatively cool.  The cooler SST does mean that the showers and thunderstorms are not as tall as they would be if the water was warmer.  The upper low west of the system is producing southerly winds which are blowing over the top of Tropical Storm Arlene.  However, since the thunderstorms are not as tall, some of the stronger upper level winds are blowing over the top of Arlene’s circulation and the vertical wind shear is not having as much of an effect as might be expected.

The environment is marginal for further intensification, but the circulation looks fairly intact at the current time.  The cool SST is limiting the amount of energy that the tropical depression can extract from the ocean.  However, since the vertical wind shear is not having as much of a negative impact on the depression, some intensification may be possible during the next 24 hours.  Eventually, the wind shear is forecast to increase and Tropical Storm Arlene is forecast to weaken.

Tropical Storm Arlene is caught in the circulation of a large low pressure system to its west.  Arlene is forecast to make a counterclockwise loop as it moves around the circulation of the larger low pressure system.  It is possible that the larger low could absorb the circulation of Tropical Storm Arlene.

Subtropical Depression 01 Transitions to Tropical Depression 01

A low pressure system designated as Subtropical Depression 01 made a tropical transition to Tropical Depression 01 on Thursday morning.  At 11:00 a.m. EDT the center of Tropical Depression 01 was located at latitude 36.1°N and longitude 40.0°W which put it about 730 miles (1170 km) west of the Azores.  The tropical depression was moving toward the northwest at 14 m.p.h. (22 km/h).  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 996 mb.

A circular ring of showers and thunderstorms developed around the center of circulation of Subtropical Depression 01.  Additional narrow rainbands organized around the core of the circulation and the convection assumed a more circularly symmetrical shape.  In addition data from satellites indicated that a weak warm core had formed at the top of the circulation.  A more circular shape and a warm core are characteristics of a tropical cyclone and the National Hurricane Center changed the classification of Subtropical Depression 01 to Tropical Depression 01 in the 11:00 a.m. EDT advisory on Thursday.

Tropical Depression 01 is in an environment that would not normally be considered favorable for a purely tropical weather system.  It is moving over water where the Sea Surface Temperature (SST) is near 19°C.  However, an upper low just to the west of the depression contains colder air.  Colder air in the upper levels is providing sufficient instability to generate showers and thunderstorms even though the SST is relatively cool.  The cooler SST does mean that the showers and thunderstorms are not as tall as they would be if the water was warmer.  The upper low west of the system is producing southerly winds which are blowing over the top of the depression.  However, since the thunderstorms are not as tall, some of the stronger upper level winds are blowing over the top of the depression’s circulation and the vertical wind shear is not having as much of an effect as might be expected.

The environment is marginal for further intensification, but the circulation looks fairly intact at the current time.  The cool SST is limiting the amount of energy that the tropical depression can extract from the ocean.  However, since the vertical wind shear is not having as much of a negative impact on the depression, some intensification may be possible during the next 24 hours.  If the depression intensifies into a tropical storm, then it would be named Arlene.  Eventually, the wind shear is forecast to increase and the depression is forecast to weaken.

Tropical Depression 01 is caught in the circulation of a large low pressure system to its west.  Tropical Depression is forecast to make a slow counterclockwise loop as it moves around the circulation of the larger low pressure system.  It is possible that the larger low could absorb the circulation of Tropical Depression 01.

Subtropical Depression 01 Develops West of the Azores

Invest 91L was reclassified as Subtropical Depression 01 by the National Hurricane Center (NHC) on Wednesday morning.  At 11:00 a.m. EDT on Wednesday the center of Subtropical Depression 01 was located at latitude 31.9°N and longitude 40.9°W which put it about 890 miles (1435 km) west-southwest of the Azores.  It was moving toward the north-northeast at 8 m.p.h.  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 995 mb.

This system was designated Invest 91L when showers and thunderstorms began to form near the center of an old occluded extratropical cyclone.  The system began to separate from the occluded front and drift toward the south-southeast.  A cut off upper level low associated with the original extratropical cyclone was rotating in a similar way to the circulation in the lower levels of Invest 91L.  So, there was not a lot of vertical wind shear.  The lack of wind shear allowed for the circulation to develop a more circular, tropical cyclone like shape.  When Invest 91L drifted toward the south-southeast it moved over slightly warmer water.  Additional energy from the ocean increased the number and strength of showers and thunderstorms.  A primary rainband wrapped about half way around the center of circulation and additional bands formed on the eastern side of the circulation.  The system developed more convection, a more circular shape and a wind field with the strongest winds closer to the center of circulation.  However, it is still under an upper low with cooler air aloft and so the system has a hybrid structure.  The hybrid structure and the lack of a well defined warm core is the reason NHC classified the system as a subtropical depression instead of designating it as a tropical depression.

Subtropical Depression 01 is in an environment that would not be favorable for the intensification of a purely tropical cyclone.  It is moving over water where the Sea Surface Temperature (SST) is near 21°C.  However, with the upper level low limiting the vertical wind shear, the SST is warm enough to support some strengthening of a subtropical cyclone.  The colder air in the upper low creates enough instability for showers and thunderstorms to develop even though they will not be as tall as they would be over warmer water in the tropics.  If the maximum sustained wind speed increases to 40 m.p.h. (65 km/h), then the system would become Subtropical Storm Arlene.  Showers and thunderstorms would have to convert enough latent energy to internal energy to generate a warm core in the middle and upper levels in order for the system to be classified as a tropical cyclone.

Subtropical Depression 01 is being steering by the upper level low underneath which it formed.  The numerical models are forecasting a slow counterclockwise loop underneath the upper low during the next few days.  Eventually, the models are forecasting that the upper low and subtropical depression will both move off toward the east.

Invest 91L Designated East of Bermuda

The core of an old occluded extratropical cyclone was designated at Invest 91L on Monday.  At 8:00 a.m. EDT on Monday the center of Invest 91L was located at latitude 32.7°N and longitude 47.1°W which put it about 1180 miles (1900 km) east of Bermuda.  Invest 91L was moving toward the south-southeast at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 75 m.p.h. (120 km/h).  The minimum surface pressure was 986 mb.

A large surface high pressure system near Europe is blocking the northeastward movement of an extratropical cyclone over the North Atlantic Ocean.  The extratropical cyclone proceeded through the normal stages of development and it matured into an occluded low during the past few days.  The occluded low has been nearly stationary over the Atlantic Ocean during that period.  Drier air wrapped around the western and southern sides of the low and the occluded front was pushed east of the core of the circulation.  More showers and thunderstorms formed closer to the center of circulation and a well defined, tightly wound circular center is apparent on the visible satellite images this morning.  The appearance of the tight circular center prompted the designation of Invest 91L.

Invest 91L is in an environment that would not be favorable for the classical development of a tropical cyclone.  It is over water where the Sea Surface Temperature (SST) is around 20°C.  However, it is possible for a transition to a tropical or subtropical cyclone to occur over colder SSTs if the air aloft is also cold enough to allow thunderstorms to develop.  It appears that there may be enough instability to allow for thunderstorms to form near the core of Invest 91L.  There is currently a cold cut off low associated with the occluded surface low over the top of Invest 91L.  Cold temperatures in the upper levels mean that Invest 91L is still an extratropical cyclone.  However, the upper low is also rotating in the same direction as the surface low.  So, there is not very much wind shear over the top of Invest 91L.

Invest 91L is forecast to move slowly southward during the next several days.  As it moves south, Invest 91L will gradually move over warmer water.  If more thunderstorms develop around the center of circulation and a warm core starts to develop, Invest 91L could be classified as a subtropical or tropical cyclone.  Since the maximum sustained wind speed is 60 m.p.h., Invest 91L could be classified as a subtropical or tropical storm if that happens.

The large surface high pressure system is forecast to continue to block the movement of Invest 91L.  Invest 91L is forecast to moved slowly toward the south or south-southeast during the next day or two.  The system could meander over the central North Atlantic Ocean during much of the week.

Tropical Storm Lisa Develops West of the Cape Verde Islands

Tropical Depression Thirteen intensified into Tropical Storm Lisa west of the Cape Verde Islands on Tuesday.  At 5:00 p.m. EDT on Tuesday the center of Tropical Storm Lisa was located at latitude 16.4°N and longitude 31.0°W which put it about 465 miles (750 km) west of the Cape Verde Islands.  Lisa was moving toward the northwest at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1004 mb.

The degree of organization of the circulation of Tropical Storm Lisa depends on the level of the atmosphere.  The low level circulation is not well organized.  There is a broad center of circulation, but it does not have a tight core of thunderstorms.  Most of the thunderstorms are east of the center of circulation.  There are also several fragmented rainbands in the eastern half of the circulation.  There are only lower clouds and a few showers in the western half of the circulation.  However, the circulation is more well organized in the upper levels.  The thunderstorms in the eastern half of the circulation are generating upper level divergence which is pumping out mass toward the northeast and toward the northwest.  It appears that the circulation could be tilted toward the northeast with height.

The environment around Tropical Storm Lisa is marginal for intensification.  Lisa is moving over water where the Sea Surface Temperature (SST) is near 28°C.  However, an upper level trough north of Lisa is producing southwesterly winds which are blowing across the tropical storm.  The winds are causing moderate vertical wind shear, which probably contributed to the asymmetrical distribution of thunderstorms.  Tropical Storm Lisa could intensify somewhat on Wednesday, if the upper level winds diminish.  When Lisa moves farther north later this week, it will move over cooler SSTs and into a region where the upper level winds are stronger.  Less energy in the upper ocean and more vertical wind shear will cause Tropical Storm Lisa to weaken later this week.

Tropical Storm Lisa is moving northwest toward a section of the subtropical ridge which is weaker.  Lisa is expected to continue to move in that general direction for the next several days.  Tropical Storm Lisa will move farther into the middle of the Atlantic Ocean and it will not threaten any land areas this week.

Tropical Storm Ian Forms in the Middle of the Atlantic

Tropical Storm Ian formed on Monday in the middle of the Atlantic Ocean.  At 11:00 a.m. EDT on Monday the center of Tropical Storm Ian was located at latitude 21.8°N and longitude 50.4°W which put it about 1140 miles (1840 km) southeast of Bermuda.  Ian was moving toward the northwest at 13 m.p.h. (21 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (95 km/h).  The minimum surface pressure was 1007 mb.

The circulation of Tropical Storm Ian is not well organized.  A large upper low west of Ian is generating strong southwesterly winds which are blowing across the top of the tropical storm.  There is a large cyclonic circulation in the lower levels, but there are no thunderstorms near the center of circulation.  The thunderstorms are forming northeast of the center in a rainband that is well removed from the core of the storm.

Tropical Storm Ian will through a hostile environment during the next several days.  Although Ian will move over water where the Sea Surface Temperature is near 29°C, the upper level trough will continue to cause strong vertical wind shear.  Ian is not likely to strengthen in the short term.  Eventually, later this week Ian will move farther from the upper level trough and it could strengthen somewhat at that time, if the low level circulation persists.

Tropical Storm Ian is moving around the western end of a subtropical ridge which is steering it toward the northwest and that general motion is expected to continue for another day or two.  When Ian moves farther north, it will turn toward the northeast and the tropical storm will begin to move faster.

Large Hurricane Gaston Prompts Tropical Storm Watch for Azores

Large Hurricane Gaston starting moving more quickly toward the northeast on Wednesday and it prompted a Tropical Storm Watch for some of the Azores.  The Tropical Storm Watch includes Flores, Corvo, Faial, Pico Gracsiosa, Sao Jorge and Terceira in the Azores.

At 8:00 p.m. EDT on Wednesday the center of Hurricane Gaston was located at latitude 35.6°N and longitude 46.5°W which put it about 1000 miles (1610 km) west of Faial in the Azores.  Gaston was  moving toward the northeast at 18 m.p.h. (30 km/h).  The maximum sustained wind speed was 105 m.p.h. (165 km/h) and there were wind gusts to 125 m.p.h. (200 km/h).  The minimum surface pressure was 969 mb.

Hurricane Gaston has a large circular eye with a diameter of 35 miles (55 km).  The eye is surrounded by a nearly complete eyewall, although the eyewall is thinner in the southwestern quadrant.  Winds to hurricane force extend out about 45 miles (70 km) from the center.  Hurricane Gaston has characteristics of an annular hurricane and the surrounding rainbands are mainly comprised of showers and shallow clouds.  The upper level divergence is inhibited over the southwestern past of the circulation, but divergence is still occurring north and east of the center.

Hurricane Gaston will be moving through an environment that will become increasingly unfavorable.  It is currently over water where the Sea Surface Temperature (SST) is near 27.5°C, but it will be moving over cooler SST during the next few days.  An upper level trough is producing southwesterly winds which are causing vertical wind shear.  The strength of the upper level winds is expected to increase.  The combination of cooler SSTs and more wind shear will weaken Gaston during the next few days.

Hurricane Gaston is being steering toward the northeast by the westerly flow in the middle latitudes.  That general motion is expected to continue.  On its anticipated track Hurricane Gaston could reach the western Azores within 48 hours.  It is expected to weaken below hurricane intensity by that time.  Because of its large size, Gaston could bring wind and rain to many of the Azores.

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.