Category Archives: Tropical Cyclones

Information about tropical cyclones

Hurricane Fernanda Intensifies Rapidly to Category 4

Hurricane Fernanda intensified rapidly to Category 4 on the Saffir-Simpson Scale on Friday.  At 5:00 p.m. EDT on Friday the center of Hurricane Fernanda was located at latitude 10.7°N and longitude 119.7°W which put it about 1060 miles (1710 km) southwest of the southern tip of Baja California.  Fernanda was moving toward the west 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 155 m.p.h. (250 km/h).  The minimum surface pressure was 960 mb.

A clear circular eye formed at the center of Hurricane Fernanda.  The eye is surrounded by a ring of very strong thunderstorms and the strongest winds are occurring in the eyewall.  Additional bands of showers and thunderstorms formed outside the core of Fernanda.  There are more bands in the eastern half of the hurricane, but the overall circulation is fairly symmetrical.  The thunderstorms in the core of Fernanda are generating strong upper level divergence which is pumping mass away from the hurricane.

Fernanda is a small hurricane.  Winds to hurricane force only extend out about 25 miles (40 km) from the center of circulation.  Winds to tropical storm force only extend out about 70 miles (110 km) from the center.  The Hurricane Intensity Index (HII) is 25.1.  The Hurricane Size Index (HSI) is 9.0 and the Hurricane Wind Intensity Size Index (HWISI) is 34.1.  The indices indicate that Hurricane Fernanda is somewhat similar in size and strength to Hurricane Charley in 2004 when Charley was approaching the southwest coast of Florida.

Hurricane Fernanda will remain in an environment very favorable for intensification for another 24 to 48 hours.  It will move over water where the Sea Surface Temperature (SST) is near 28.5°C.  The upper level winds are weak and there is little vertical wind shear.  Hurricane Fernanda has a chance to intensify into a Category 5 hurricane on the Saffir-Simpson Scale before it moves into a less favorable environment.  When a hurricane becomes as intense as Hurricane Fernanda is, an outer rainband can wrap around the eye and an eyewall replacement cycle can occur.  If an eyewall replacement cycle occurs in Hurricane Fernanda, then fluctuations in intensity may also happen.  Eventually Fernanda will move over cooler SSTs and the hurricane will start to weaken.

Hurricane Fernanda is moving south of a subtropical ridge and the ridge is steering the hurricane a little south of due west.  A general westward motion is forecast to continue during the next few days.  On its anticipated track Hurricane Fernanda will continue to move farther away from Mexico.  Fernanda could approach Hawaii by the end of next week.

Fernanda Rapidly Intensifies Into a Hurricane

Former Tropical Storm Fernanda rapidly intensified into a hurricane on Thursday.  At 5:00 p.m. EDT on Thursday the center of Hurricane Fernanda was located at latitude 11.2°N and longitude 116.0°W which put it about 900 miles (1450 km) south-southwest of the southern tip of Baja California.  Fernanda was moving toward the west at 12 m.p.h. (19 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 990 mb.

A primary rainband wrapped around the center of circulation and an eye appeared intermittently on visible satellite images on Thursday afternoon.  The improved organization of the inner core of Fernanda allowed it to intensify rapidly into a hurricane.  The distribution of thunderstorms become more symmetrical and circulation exhibited a more circular appearance.  Thunderstorms in the inner core began to generate strong upper level divergence which pumped out mass in all directions.  The divergence of mass allowed the surface pressure to decrease and the wind speeds to increase rapidly.

Hurricane Fernanda will move through an environment that will be favorable for further intensification during the next two days.  Fernanda will move over water where the Sea Surface Temperature (SST) is near 29°C.  An upper level ridge northeast of Fernanda is producing easterly winds which are blowing toward the top of the hurricane.  However, the speed of the upper level winds decreased on Thursday and there is less vertical wind shear.  A combination of a well organized inner core, warm SSTs and reduced vertical wind shear resulted in rapid intensification of Fernanda into a hurricane.  Rapid intensification could continue for another 24 to 36 hours and Fernanda is forecast to become a major hurricane on Friday.

A subtropical ridge to the north of Fernanda is steering the hurricane toward the west and a general westerly motion is expected to continue for several more days.  On its anticipated track Hurricane Fernanda will move farther away from Mexico.

TD 6E Strengthens Into Tropical Storm Fernanda

Tropical Depression Six-E strengthened into Tropical Storm Fernanda on Wednesday.  At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Fernanda was located at latitude 11.9°N and longitude 113.1°W which put it about 790 miles (1270 km) south-southwest of the southern tip of Baja California.  Fernanda was moving toward the west at 9 m.p.h. (15 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 1004 mb.

Thunderstorms on the western side of the center of Tropical Storm Fernanda increased on Wednesday night.  Several bands of showers of thunderstorms formed in the western half of the circulation, but the distribution of convection remained asymmetrical.  There were few showers and thunderstorms in the eastern half of the circulation.  The thunderstorms in the western half of the were generating upper level divergence which was pumping out mass to the west of Tropical Storm Fernanda.

Tropical Storm Fernanda is currently in an environment that is moderately favorable for intensification.  It is moving over water where the Sea Surface Temperature (SST) is near 29.5°C.  An upper level ridge north of Fernanda is producing easterly winds which are blowing toward the top of the tropical storm.  Those winds are causing moderate vertical wind shear and the shear may be the cause of the asymmetrical distribution of thunderstorms.  Fernanda is likely to move into an area where the upper level winds are weaker and the shear will decrease.  Warm SSTs and less wind shear should allow Tropical Storm Fernanda to intensify into a hurricane later this week.  Once an eye forms, a period of rapid intensification will be possible and Fernanda could eventually become a major hurricane.

A subtropical ridge north of Fernanda is steering the tropical storm westward and a general westerly motion is expected to continue for the next few days.  On its anticipated track Tropical Storm Fernanda will move away from Mexico and it could move into the Central Pacific in a few days.

Tropical Depression Six-E Forms West of Mexico

The Eastern North Pacific basin continues to be active tropically.  Tropical Depression Six-E formed west of Mexico on Tuesday.  At 11:00 p.m. EDT on Tuesday the center of Tropical Depression Six-E was located at latitude 12.2°N and longitude 109.9°W which put it about 740 miles (1190 km) south of the southern tip of Baja California.  It was moving toward the west at 12 m.p.h. (19 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 1007 mb.

A center of circulation consolidated within a large area of thunderstorms south of Baja California on Tuesday.  A primary band of showers and thunderstorms wrapped around the western and southern sides of the center of circulation.  Additional bands of showers and thunderstorms were beginning to form north and west of the center.  There were not many showers and storms in the eastern half of the circulation.  The thunderstorms near the core of the circulation were beginning generate upper level divergence which was pumping away from depression.

Tropical Depression Six-E will move through an environment that will be favorable for intensification.  It will move over water where the Sea Surface Temperature (SST) is near 29°C.  Tropical Depression Six-E is near the western end of an upper level ridge and the upper level winds are relatively weak.  Warm SSTs and little vertical wind shear should allow the depression to strengthen during the next several days.  Tropical Depression Six-E is likely to become a tropical storm on Wednesday and it could become a hurricane later this week.

Tropical Depression Six-E is moving south of a subtropical ridge which is steering the depression toward the west.  The subtropical ridge is expected to continue to steer the depression toward the west during the next few days.  On its anticipated track the depression is expected to move away from the coast of Mexico.

Eugene Becomes a Hurricane Southwest of Baja California

Tropical Storm Eugene strengthened rapidly into a hurricane on Saturday as it moved southwest of Baja California.  At 11:00 p.m. EDT on Saturday the center of Hurricane Eugene was located at latitude 14.4°N and longitude 113.5°W which put it about 630 miles (1020 km) south-southwest of the southern tip of Baja California.  Eugene was moving toward the northwest at 8 m.p.h. (13 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 990 mb.

A primary raindband wrapped around the center of Hurricane Eugene on Saturday and an eye formed at the center of circulation.  The eye had a diameter of 30 miles (50 km).  Additional bands of showers and thunderstorms were revolving around the core of the circulation.  Thunderstorms were generating well developed upper level divergence which was pumping mass away in all directions.  The circulation of Hurricane Eugene was symmetrical and well organized.

Hurricane Eugene was moving over water where the Sea Surface Temperature (SST) was near 29°C.  Eugene was underneath the western end of an upper level ridge.  The ridge was producing southerly winds which were blowing toward the top of the hurricane, but the vertical wind shear was not very strong.  Eugene is likely to intensify on Sunday.  It will gradually move over cooler SSTs and Hurricane Eugene will move over water where the water is cooler than 26°C on Monday.  When Eugene reaches the cooler SSTs, it will begin a steady weakening trend.

Hurricane Eugene is moving around the western end of a subtropical ridge which is steering it toward the northwest.  Eugene is expected to continue to move toward the northwest during the next several days.  On its anticipated track Hurricane Eugene will move parallel to the west coast of Baja California.

Tropical Storm Eugene Forms South of Baja California

A distinct center of circulation consolidated within a broader area of low pressure south of Baja California on Friday and the National Hurricane Center classified the system as Tropical Storm Eugene.  At 5:00 p.m. EDT on Friday the center of Tropical Storm Eugene was located at latitude 11.9°N and longitude 111.2°W which put it about 765 miles (1230 km) south of the southern tip of Baja California.  Eugene was moving toward the northwest at 8 m.p.h. (13 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 1006 mb.

The circulation of Tropical Storm Eugene is large and there are numerous bands of showers and thunderstorms rotating around the center of circulation.  A primary rainband is wrapping around the southern and eastern sides of the center and the strongest winds are occurring northeast of the center of circulation.  The circulation is circular and symmetrical.  Thunderstorms around the core of Eugene are beginning to generate upper level divergence which is pumping out mass in all directions.

Tropical Storm Eugene will move through an environment that is favorable for intensification.  Eugene will move over water where the Sea Surface Temperature is near 29°C.  The upper level winds over Tropical Storm Eugene are relatively weak and there is not a lot of vertical wind shear.  The circulation of Tropical Storm Eugene will continue to consolidate and it is likely to intensify during the weekend.  It is likely to become a hurricane and it could intensify rapidly if an eye forms.

Tropical Storm Eugene is moving near the western end of a subtropical ridge which is steering it toward the northwest.  A generally northwesterly motion is expected to continue during the next few days.  On its anticipated track Tropical Storm Eugene would move parallel to the west coast of Baja California and the center would remain west of the coast.

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.

Tropical Storm Nanmadol Nearing Kyushu

Tropical Storm Nanmadol was quickly nearing Kyushu on Monday.  At 1:00 p.m. EDT on Monday the center of Tropical Storm Nanmadol was located at latitude 31.0°N and longitude 127.4°E which put it about 215 miles (345 km) southwest of Sasebo, Japan.  Nanmadol was moving toward the north-northeast at 24 m.p.h. (39 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 986 mb.

The structure of Tropical Storm Nanmadol was still consistent with its designation of a tropical cyclone, but there were signs that it could be about to start the transition to an extratropical cyclone.  There was a core of thunderstorms around the center of circulation.  The strongest winds were occurring in the inner core which extended out about 25 miles (40 km) from the center.  Several rainbands were on the eastern side of the circulation.  There were far fewer showers and thunderstorms in the western half of the circulation.  There were some indications that Nanmadol could be pulling cooler, drier, more stable air into the western side of the tropical storm.

Tropical Storm Nanmadol has probably reached its maximum intensity and it is likely to weaken during the next two days.  Nanmadol is currently over water where the Sea Surface Temperature is near 27°C.  However, it has reached the upper level westerly in the middle latitudes and the vertical wind shear is increasing.  Nanmadol will weaken faster when it moves across Japan.

The westerly winds in the middle latitudes have turned Tropical Storm Nanmadol toward the north-northeast.  As Nanmadol moves farther north, the speed of the westerlies will increase and the tropical storm is forecast to move quickly toward the east-northeast across southern Japan.  On its anticipated track, Tropical Storm Nanmadol will reach Kyushu in a few hours.  Nanmadol will also move over Shikoku and Honshu.  Tropical Storm Nanmadol will bring a brief period of gusty winds and the potential for locally heavy rain when it moves across southern Japan.

Tropical Storm Nanmadol Brings Wind and Rain to Southern Ryukyu Islands

Tropical Storm Nanmadol brought wind and rain to the southern Ryukyu Islands on Sunday.  At 11:00 a.m. EDT on Sunday the center of Tropical Storm Nanmadol was located at latitude 24.4°N and longitude 124.7°E which put it about 40 miles (65 km) east of Ishigaki, Japan.  Nanmadol was moving toward the north-northwest at 21 m.p.h. (34 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 998 mb.

The core of Tropical Storm Nanmadol continued to organize on Sunday.  A ring of thunderstorms wrapped tightly around the center of circulation.  Additional bands of showers and thunderstorms formed outside the core.  Thunderstorms were beginning to generate more upper level divergence which was pumping out mass in all directions.  The circulation of Tropical Storm Nanmadol was fairly small.  Winds to tropical storm force only extend out about 70 miles (110 km) from the center.

Tropical Storm Nanmadol will be in an environment that is very favorable for intensification for about another 24 hours.  Nanmadol will be moving over water where the Sea Surface Temperature (SST) is near 29°C.  The circulation of Tropical Storm Nanmadol is underneath the center of an upper level ridge and the upper level winds are very weak.  Warm SSTs and almost no vertical wind shear will permit Tropical Storm Nanmadol to intensify during the next day and there could be a period of rapid intensification.  Nanmadol could strengthen into a typhoon before it reaches a less favorable environment.  The tropical storm will move over cooler SSTs and it will move into an area of stronger upper level westerly winds in a couple of days.  Nanmadol will begin to weaken when that happens.

Tropical Storm Nanmadol is moving around the western end of a subtropical ridge which is steering it toward the north.  A general northward motion is expected to continue for about another 24 hours.  Nanmadol will reach the westerly winds in the middle latitudes in about a day and those winds will turn it toward the northeast.  On its anticipated track the center of Tropical Storm Nanmadol will pass west of Okinawa.  Nanmadol could approach Kyushu in about 36 hours.  Tropical Storm Nanmadol will continue to cause gusty winds and locally heavy rain over the southern Ryukyu Islands for another 12 to 24 hours.