Tag Archives: the Azores

Tropical Depression Nineteen Forms East of Bermuda

Tropical Depression Nineteen formed east of Bermuda on Monday.  At 10:00 a.m. EST on Monday the center of Tropical Depression Nineteen was located at latitude 29.5°N and longitude 50.4°W which put it about 875 miles east of Bermuda.  It was moving toward the north-northeast at 3 m.p.h. (5 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 1013 mb.

A small low pressure system has been meandering over the Atlantic Ocean between Bermuda and the Azores.  More showers and thunderstorms formed near the center of the the low and the circulation became more circular.  Because the low pressure system developed the characteristics of a tropical cyclone, the National Hurricane Center designated the system as Tropical Depression Nineteen on Monday morning.

The circulation of Tropical Depression Nineteen is being affected by vertical wind shear.  An upper level low located to the northwest of the system is producing easterly winds which are blowing across the top of the depression.  Those winds are producing moderate vertical wind shear shear which is tilting the upper portion of the circulation to the east.  The surface center of circulation was exposed on visible satellite images.  Most of the showers and thunderstorms were occurring to the east of the center.

Tropical Depression Nineteen is forecast to intensify into a tropical storm.  The depression will move over water where the Sea Surface Temperature is near 25.5°C, which is marginally warm enough to support intensification.  The upper level low will continue to produce vertical wind shear which will inhibit intensification during the next 12 to 24 hours.  The shear is forecast to decrease on Tuesday and Tropical Depression Nineteen could strengthen into a tropical storm before it moves over colder water.

Tropical Depression Nineteen is currently in an area where the steering currents are weak.  The circulation around the upper level low to the northwest of the Tropical Depression is being deflected around an upper level ridge to the east of the depression.  Some of the flow is turning northward and the rest of the flow is turning toward the south.  The orientation of the upper low and ridge is forecast to change and the two systems are forecast to steer the depression toward the northeast later this week.  However, if the wind shear stays strong enough to prevent the circulation of the depression from growing vertically, then the winds in the lower level could steer the depression more toward the west.

Ophelia Strengthens to Major Hurricane South of the Azores

Hurricane Ophelia strengthened into a Category 3 hurricane on the Saffir-Simpson Scale on Saturday morning as it moved south of the Azores.  That made Ophelia a major hurricane.  At 11:00 a.m. EDT on Saturday the center of Hurricane Ophelia was located at latitude 34.8°N and longitude 26.6°W which put it about 220 miles (355 km) south of the Azores.  Ophelia was moving toward the northeast at 25 m.p.h. (40 km/h).  The maximum sustained wind speed was 115 m.p.h. (185 km/h) and there were wind gusts to 135 m.p.h. (220 km/h).  The minimum surface pressure was 960 mb.

It is very unusual to have such a strong hurricane near the Azores, but Ophelia contains all of the elements of a major hurricane.  There is a circular eye at the center of circulation.  The eye is surrounded by a ring of strong thunderstorms and the strongest winds are occurring in that ring of storms.  Well formed rainbands exists in the outer portions of the circulation.  Storms in the core of Ophelia are generating upper level divergence which is pumping mass away to the northeast of the hurricane.  Winds to hurricane force extend out about 40 miles (65 km) from the center of circulation.  Winds to tropical storm force extend out about 125 miles (205 km) from the center.

Hurricane Ophelia is moving over water where the Sea Surface Temperature is near 25°C.  Normally, water at that temperature would be considered to be too cool to support the development of a major hurricane.  However, the temperature of the air in the upper troposphere is also cool and so the atmosphere is unstable enough to allow for the development of deep convection.  An upper level trough west of Ophelia is producing southwesterly winds which are blowing toward the top of the circulation.  There are also southwesterly winds in the lower and middle levels of the atmosphere and so the vertical wind shear is not strong enough to inhibit intensification

Hurricane Ophelia will be moving over cooler water and it is likely to weaken gradually during the next several days.  When Ophelia moves over the cooler water it will make a transition to an extratropical cyclone.  The size of the circulation will increase during the transition.  Hurricane Ophelia will evolve into a large very powerful extratropical cyclone during the next several days.

The trough west of Ophelia is steering the hurricane toward the northeast.  Hurricane Ophelia is expected to turn more toward the north during the next two or three days.  On its anticipated track Hurricane Ophelia will pass east of the Azores later today.  The strong extratropical cyclone that Ophelia will transition into could approach Ireland and the United Kingdom by Monday morning.  That cyclone will bring very strong winds and heavy rain to that region.

Hurricane Ophelia Moves Closer to the Azores

Hurricane Ophelia moved closer to the Azores on Friday.  At 5:00 p.m. EDT on Friday the center of Hurricane Ophelia was located at latitude 32.3°N and longitude 31.8°W which put it about 480 miles (770 km) southwest of the Azores.  Ophelia was moving toward the east-northeast at 13 m.p.h. (20 km/h).  The maximum sustained wind speed was 100 m.p.h. (160 km/h) and there were wind gusts to 120 m.p.h. (195 km/h).  The minimum surface pressure was 971 mb.

Despite moving over slightly cooler water, Hurricane Ophelia maintained its structure and intensity on Friday.  There was a small circular eye at the center of circulation, although there appeared to be a break on the northwest side of the ring of thunderstorms around the eye.  Thunderstorms in the core of Ophelia were generating upper level divergence which was pumping away mass.  Bands of showers and thunderstorms were revolving around the core of Hurricane Ophelia.  The stronger rainbands were in the eastern half of the circulation.  Winds to hurricane force extended out about 25 miles (40 km) from the center of circulation.  Winds to tropical storm force extended out about 100 miles (160 km) from the center.

Hurricane Ophelia will move through an environment that is capable of supporting a strong cyclone.  Ophelia will move over water where the Sea Surface Temperature is near 25°C.  Normally, that water would be too cool to support a strong hurricane.  However, the temperature in the upper levels of the atmosphere is also cool and that is keeping the atmosphere unstable enough to allow for thunderstorms to develop.  The speed of the winds in Hurricane Ophelia is likely to decrease gradually during the next several days.

When Hurricane Ophelia moves farther north, it will move into a cooler environment with stronger westerly winds in the upper levels.  A cooler environment with more vertical wind shear will cause the structure of Hurricane Ophelia change into the structure of an extratropical cyclone.  The area of stronger winds will expand and the cyclone will become much larger.

Hurricane Ophelia is being steered toward the east-northeast by westerly winds in the middle levels.  A trough will approach Hurricane Ophelia from the west.  Southwesterly winds ahead of the trough will carry Ophelia more toward the north in about 36 hours.  On its anticipated track the center of Hurricane Ophelia will move south of the Azores on Saturday.  Ophelia could bring gusty winds and rain to the Azores when it moves by those islands.  The strong extratropical cyclone that evolves from Hurricane Ophelia could approach Ireland and the United Kingdom on Monday.  That cyclone could bring very strong winds and heavy rain to that region.

Ophelia Strengthens Into a Hurricane Southwest of the Azores

Tropical Storm Ophelia strengthened into a hurricane southwest of the Azores on Wednesday.  At 11:00 p.m. EDT on Wednesday the center of Hurricane Ophelia was located at latitude 30.0°N and longitude 35.7°W which put it about 745 miles (1195 km) southwest of the Azores.  Ophelia was moving toward the northeast at 3 m.p.h.  The maximum sustained wind speed was 85 m.p.h. (140 km/h) and there were wind gusts to 100 m.p.h. (160 km/h).  The minimum surface pressure was 986 mb.

The circulation of Hurricane Ophelia became more circular and symmetrical on Wednesday.  A circular eye developed at the center of circulation.  Thunderstorms in the ring around the eye became taller.  Additional bands of showers and thunderstorms were revolving around the core of Hurricane Ophelia.  Thunderstorms in the core were producing upper level divergence which was pumping mass away to the east of the hurricane.  Winds to hurricane force extended out about 25 miles (40 km) from the center of circulation.  Winds to tropical storm force extended out about 70 miles (110 km) from the center.

Hurricane Ophelia will be moving through an environment that could support further intensification on Thursday.  Ophelia will move over water where the Sea Surface Temperature is near 26.5°C.  Ophelia is in an area of weaker upper level winds.  It is north of the subtropical jet stream and it is south of the stronger westerly winds in the middle latitudes.  As a result the vertical wind shear is minimal.  The combination of warm water and little shear allowed Ophelia to intensify into a hurricane and it could strengthen further on Thursday.

Hurricane Ophelia is in an area of weak westerly winds which are steering the hurricane slowly toward the east.  An upper level trough will approach Ophelia from the west and the trough will start to pull the hurricane toward the northeast more quickly later this week.  On its anticipated track Hurricane Ophelia could approach the Azores in two or three days.

Tropical Storm Ophelia Forms Over Eastern Atlantic

The busy 2017 Atlantic hurricane season continued when Tropical Storm Ophelia formed over the eastern Atlantic Ocean on Monday.  At 5:00 p.m. EDT on Monday the center of Tropical Storm Ophelia was located at latitude 31.5°N and longitude 39.6°W which put it about 845 miles (1355 km) west-southwest of the Azores.  Ophelia was moving toward the northeast at 3 m.p.h. (5 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 1005 mb.

Thunderstorms formed on Monday near the center of a low pressure system which had been lingering over the eastern Atlantic Ocean and the National Hurricane Center designated the system as Tropical Storm Ophelia.  The thunderstorms formed near the eastern side of the center and several bands of showers and thunderstorms formed in the rest of the eastern half of the circulation.  There were fewer thunderstorms in the western half of Ophelia.  The thunderstorms near the center of circulation were generating upper level divergence which was pumping mass away to the east of the tropical storm.

Tropical Storm Ophelia is an environment that is somewhat favorable to intensification.  Ophelia is moving over water where the Sea Surface Temperature (SST) is near 27°C.  It is near the axis of an upper level trough which is oriented east to west over the Atlantic Ocean.  The trough is producing westerly winds which are blowing toward the top of the circulation and those winds are causing some vertical wind shear.  However, since Ophelia is over water where the SST is 27°C, the clouds are not rising as far into the atmosphere as they would if the water was warmer and some of the upper level winds are blowing completely over the top of the circulation of the tropical storm.  So, the vertical wind shear is not as significant as it could be if the top of Ophelia was higher in the atmosphere.  Tropical Storm Ophelia is likely to strengthen during the next several days and it could eventually become a hurricane.

Since Tropical Storm Ophelia is near the axis of the upper level trough, the steering winds are weaker.  The westerly flow is pushing Ophelia slowly toward the northeast.  The orientation of the trough is forecast to change during the next day or two and Ophelia is expected to move more toward the east-southeast.  On its anticipated track Tropical Storm Ophelia is expected to meander over the eastern Atlantic Ocean for several more days.

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.