Tag Archives: Bermuda

Tropical Depression Four Develops East of the Lesser Antilles

Tropical Depression Four developed east of the Lesser Antilles on Wednesday night.  At 11:00 p.m. EDT on Wednesday the center of Tropical Depression Four was located at latitude 12.8°N and longitude 38.4°W which put it about 1545 (2485 km) east of the Lesser Antilles.  The depression was moving toward the west-northwest at 14 m.p.h. (22 km/h).  The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were wind gusts to 40 m.p.h. (65 km/h).  The minimum surface pressure was 1009 mb.

A larger area of thunderstorms formed and persisted on the western side of a tropical disturbance formerly designated as Invest 94L on Wednesday and the National Hurricane Center classified the system as Tropical Depression Four.  The distribution of thunderstorms is still asymmetrical.  Most of the stronger storms are developing in the western half of the circulation.  The thunderstorms in the western part of the circulation were beginning to generate upper level divergence.  There were few thunderstorms in the eastern half of the depression and the vertical structure of the circulation could be tilted to the west with height.

Tropical Depression Four will be moving through an environment that contains both positive and negative factors for intensification.  The depression will move over water where the Sea Surface Temperature is near 27°C.  So, there is sufficient energy in the upper ocean to support intensification.  An upper level ridge is producing easterly winds which are blowing toward the top of the circulation.  Those winds could be causing the circulation to tilt toward the west with height.  Moderate vertical wind shear could inhibit intensification.  Drier air is north of the tropical depression.  If the depression remains south of the drier air and if the vertical wind shear does not become too strong, then the depression could strengthen.  Alternatively, if the depression pulls in drier air and/or the vertical shear increases, then the depression could weaken back to a tropical wave.

The subtropical ridge over the Atlantic Ocean is steering Tropical Depression Four toward the west-northwest.  A general west-northwesterly motion is expected for the next several days.  The actual track will also have a significant effect on the future intensity of Tropical Depression Four. If the depression moves on a more southerly track, it will stay south of the drier air and it would have a greater opportunity to intensify.  If the depression moves farther to the north, it will move into the drier air and will be more likely to weaken,

Invest 94L Likely to Develop East of Lesser Antilles

A tropical disturbance currently designated as Invest 94L is likely to develop into a tropical cyclone east of the Lesser Antilles.  The National Hurricane Center’s probability of formation of a tropical cyclone from this system during the next five days is 70%.  At 2:00 p.m. EDT on Monday the center of Invest 94L was located at latitude 8.7°N and longitude 32.7°W which put it about 1830 miles (2950 km) east of the Lesser Antilles.  It was moving toward the west at 4 m.p.h. (6 km/h).  The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were wind gusts to 40 m.p.h. (65 km/h).  The minimum surface pressure was 1011 mb.

Invest 94L consists of a broad area of low pressure, but it has not developed a well organized inner core.  The initial area of low pressure consisted of a counterclockwise rotation associated with a tropical wave that moved over the eastern Atlantic Ocean.  The initial low slowed down as it was moving westward and a second tropical wave caught up to it.  The thunderstorms from the two waves appear to be merging into a single system.  An area of showers and thunderstorms on the northern and western sides of the surface low was part of the first tropical wave.  Other bands of showers and thunderstorms south and east of the low are associated with the second tropical wave.  If the broad low pressure system can collect the rotation from the two tropical waves, it could strengthen the surface low.

Invest 94L will move through an environment that will be favorable for the development of a tropical cyclone.  It will move over water where the Sea Surface Temperature (SST) is near 28°C.  There are easterly winds blowing at multiple levels in the atmosphere and there is little vertical winds shear.  The existence of a surface low pressure system, warm SSTs and little vertical wind shear are the primary ingredients for the development of a tropical cyclone.  That is the reason why there is strong probability that Invest 94L will develop into a tropical depression or a tropical storm.

Invest 94L will be steered by the subtropical high pressure system over the Atlantic Ocean.  A general westerly or west-northwesterly track is forecast during the next few days.  There is still significant uncertainty about the ultimate track and intensity of this system beyond that time frame.  It will need to be monitored closely as it moves west.

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.

Low Pressure Develops East of the Bahamas

An area of low pressure developed east of the Bahamas and the system was designated as Invest 90L on Sunday afternoon.  At 5:00 p.m. EDT on Sunday the center of Invest 90L was located at latitude 24.0°N and longitude 71.0°W which put it about 260 miles (420 km) east of the Bahamas.  Invest 90L was moving toward the northwest at 11 m.p.h. (17 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. (80 km/h).  The minimum surface pressure was 1009 mb.

The circulation of Invest 90L consists of a large asymmetrical low pressure system.  Most of the showers and thunderstorms are occurring northeast of the center of circulation.  Those showers and thunderstorms are being generated by convergence of winds from a large high pressure system over the north Atlantic Ocean into the area of low pressure.  A swirl of low clouds has emerged on the southwestern side of the low, but it is unclear if this is the actual center of circulation or is just a transient mesoscale feature.  A strong pressure gradient between the high pressure system and the low is producing an area of winds to tropical storm force northeast of the center of the low.  The winds are weaker in other parts of the circulation.

Invest 90L is in an environment that is mostly unfavorable for tropical cyclones.  It is moving over water where the Sea Surface Temperature is near 25°C.  So, there is less energy in the upper ocean to support tropical development.  An upper level trough over the southeastern U.S. is producing strong southwesterly winds which are blowing across the top of Invest 90L.  Those winds are producing strong vertical wind shear.  Marginal Sea Surface Temperatures and strong vertical wind shear make the classical development of a tropical cyclone unlikely.  However, the temperature in the upper troposphere is also cold and there may be enough instability in the atmosphere to produce thunderstorms.  If the wind shear decrease, then more thunderstorms could develop closer to the center of circulation and a subtropical cyclone could form.

The high over the north Atlantic is blocking northward movement of Invest 90L and the high is steering it toward the northwest.  A general northwesterly motion is expected to continue for another day or so.  Eventually the high will move off to the east and Invest 90L will start to move toward the northeast.  On its anticipated track Invest 90L will stay east of the U.S. and the Bahamas.  Invest 90L could pass close to Bermuda and it has the potential to bring gusty winds.

Hurricane Nicole Bringing Strong Winds and Heavy Rain to Bermuda

Hurricane Nicole is bringing strong winds and heavy rain to Bermuda on Thursday morning.  At 11:00 a.m. EDT on Thursday the center of Hurricane Nicole was located at latitude 32.3°N and longitude 64.6°W which put it about 10 miles (15 km) east of Bermuda.  Nicole was moving toward the northeast at 16 m.p.h. (26 km/h).  The maximum sustained wind speed was 120 m.p.h. (195 km/h) and there were wind gusts to 140 m.p.h. (225 km/h).  The minimum surface pressure was 961 mb.  A Hurricane Warning remains in effect for Bermuda.

Nicole is a large powerful hurricane.  Winds to hurricane force extend out about 65 miles (105 km) from the center of circulation.  Winds to tropical storm force extend out about 180 miles (290 km) from the center.  The diameter of the eye is approximately 35 miles (55 km).

A weather station on Pearl Island reported sustained winds to 87 m.p.h. (141 km/h) with wind gusts to 119 m.p.h. (191 km/h).  An elevated weather station at Commissioner’s Point reported sustained winds to 92 m.p.h. (148 km/h) and wind gusts to 122 m.p.h. (196 km/h).

Hurricane Nicole is moving toward the northeast at 16 m.p.h. (26 km/h).  So, it will take approximately two hours for the eye of Hurricane Nicole to move across Bermuda.  After the eye passes, hurricane force winds in the southern half of Nicole will affect Bermuda.  The winds should gradually diminish later today when Hurricane Nicole moves northeast of Bermuda.

Powerful Major Hurricane Nicole Nearing Bermuda

Hurricane Nicole intensified into a powerful major hurricane late on Thursday as it moved closer to Bermuda.  At 11:00 p.m. EDT on Thursday the center of Hurricane Nicole was located at latitude 30.1°N and longitude 66.4°W which put it about 180 miles (290 km) south-southwest of Bermuda.  Nicole was moving toward the north-northeast at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 130 m.p.h. (215 km/h) and there were wind gusts to 160 m.p.h. (260 km/h).  The minimum surface pressure was 950 mb.  Nicole is a Category 4 hurricane on the Saffir-Simpson Scale.  A Hurricane Warning is in effect for Bermuda.

Hurricane Nicole intensified very rapidly during the past 12 hours.  The maximum sustained wind speed increased from 100 m.p.h. (160 km/h) to 130 m.p.h. (215 km/h) during that time period.  The minimum surface pressure decreased from 970 mb to 950 mb at the same time.  Hurricane Nicole now has a large circular eye with a diameter of 35 m.p.h. (55 km).  Hurricane Nicole also increased in size as it intensified.  Winds to hurricane force now extend out 65 miles (105 km) from the center of circulation.  Wind to tropical storm force extend out 160 miles (260 km) from the center.

Nicole is a large powerful hurricane. The Hurricane Intensity Index (HII) is 25.1.  The Hurricane Size Index (HSI) is 20.6 and the Hurricane Wind Intensity Size Index (HWISI) is 45.7.  The indices indicate that Hurricane Nicole is capable of causing widespread significant wind damage.

Southwesterly winds on the eastern side of a upper level trough will steer Hurricane Nicole toward the northeast.  When Nicole moves further north, westerly winds will steer it more toward the northeast.  On its anticipated track the core of Hurricane Nicole will reach Bermuda on Thursday morning.  Nicole has the potential to be a very destructive hurricane.

Nicole Strengthens Into a Hurricane, Warning for Bermuda

Tropical Storm Nicole intensified into a hurricane on Tuesday afternoon and a Hurricane Warning was issued for Bermuda.  At 5:00 p.m. EDT on Tuesday the center of Hurricane Nicole was located at latitude 27.4°N and longitude 66.4°W which put it about 350 miles (565 km) south-southwest of Bermuda.  Nicole was moving toward the northwest at 5 m.p.h. (8 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 980 mb.

The organization of the circulation of Hurricane Nicole improved rapidly on Tuesday afternoon.  The primary rainband wrapped around the center of circulation and an eye developed.  The eye currently has a diameter of about 30 miles (48 km).  A ring of strong thunderstorms surrounds the eye.  Those thunderstorms are producing well developed upper level divergence which is pumping out mass in all directions.  Additional rainbands are developing in the rest of the circulation.  Nicole is a relatively small hurricane.  Hurricane force winds only extend out about 35 miles (55 km) from the center and tropical storm force winds on extend out about 120 miles (195 km) from the center.

The environment around Hurricane Nicole became much more favorable on Tuesday afternoon.  The winds in the upper level weakened and the vertical wind shear diminished.  The weaker upper level winds also allowed the upper level divergence to pump out more mass and the pressure decreased 10 mb in six hours on Tuesday afternoon.  Less vertical wind shear allowed Hurricane Nicole to extract energy more efficiently from the ocean.  Hurricane Nicole is moving over water where the Sea Surface Temperature is near 28.5°C.  Nicole is likely to intensify for another 36 to 48 hours.  So, Hurricane Nicole will continue to intensify and it could intensify rapidly.  Nicole could be a major hurricane by the time it nears Bermuda.

Nicole is moving around the western end of a subtropical high pressure system which is steering the hurricane toward the northwest.  When Hurricane Nicole reaches the western end of the high, it will turn more toward the north.  As Hurricane Nicole moves farther north, the westerly winds in the middle latitudes will turn it toward the northeast.  On its anticipated track, Hurricane Nicole could approach Bermuda on Thursday morning.  It could be a major hurricane at that time.