Category Archives: Tropical Cyclones

Information about tropical cyclones

Tropical Storm Ida Forms West of the Cape Verde Islands

The circulation within a tropical disturbance west of the Cape Verde Islands organized on Friday and it was classified as Tropical Storm Ida by the National Hurricane Center.  At 11:00 p.m. EDT on Friday the center of Tropical Storm Ida was located at latitude 13.7°N and longitude 37.5°W which put it about 915 miles (1470 km) west of the Cape Verde Islands.  Ida was moving toward the northwest at 7 m.p.h. (11 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.

Tropical Storm Ida has a much larger circulation than many of the tropical storms that have formed over the eastern Atlantic Ocean in 2015.  It has a well formed spiral rainband that curls around the southern and eastern side of the center of circulation.  The upper level winds over Ida are not very strong and upper level divergence is beginning to occur in all directions.  Ida is over water where the Sea Surface Temperature is near 28°C.  There is little vertical wind shear and the environment favors intensification.   A period of rapid intensification is possible if the inner core organizes and an eye and eyewall develop.  Ida has a chance to become a hurricane during the next several days.

A subtropical ridge north of Ida is steering the tropical storm toward the northwest and that general steering pattern is expected to continue for the next day or two.  The guidance from the numerical models is less consistent for early next week and that means there is more uncertainty about the longer term track for Ida.

 

Typhoon Krovanh Nearing Iwo To

Typhoon Krovanh continued to intensify on Thursday and it is now the equivalent of a Major Hurricane.  At 11:00 p.m. EDT on Thursday the center of Typhoon Krovanh was located at latitude 24.1°N and longitude 142.5°E which put it about 105 miles (170 km) southeast of Iwo To.  Krovanh was moving toward the north-northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 120 m.p.h. (195 km/h) and there were wind gusts to 150 m.p.h. (240 km/h).  The minimum surface pressure was 935 mb.  The weather station on Iwo To is currently reporting sustained winds of 33 m.p.h. (53 km/h) with wind gusts to 48 m.p.h. (77 km/h).

Typhoon Krovanh has probably reached its peak intensity.  It may be pulling in some drier air from the northwest.  It also looks like an upper level trough near Japan is beginning to cause southwesterly winds over the top of the typhoon.  There is a gap in the eyewall on the south side and clouds are beginning to obscure the eye on satellite imagery.  Vertical wind shear will increase as Krovanh moves farther north and it gets closer to the upper level trough.  Krovanh will also start to move over cooler Sea Surface Temperatures which will increase the rate at which it weakens.

Typhoon Krovanh is moving around the western end of the subtropical ridge that has been steering it.  It will start to turn toward the northeast on Friday as the upper level trough begins to steer the typhoon.  On its anticipated track the center of Krovanh will pass within about 50 to 60 miles (80 to 95 km) of Iwo To during the next few hours and then it will be very near Chichi Jima in about 18 hours.  Krovanh could cause gusty winds, heavy rain and large waves as it passed near those two islands.

Krovanh Becomes a Typhoon Southeast of Iwo To

Krovanh continued to intensify rapidly on Wednesday and it reached typhoon status.  At 11:00 p.m. EDT on Wednesday the center of Typhoon Krovanh was located at latitude 21.5°N and longitude 144.5°E which put it about 330 miles (530 km) southeast of Iwo To.  Krovanh was moving toward the northwest at 13 m.p.h. (21 km/h).  The maximum sustained wind speed was 90 m.p.h. (145 km/h) and there were wind gusts to 115 m.p.h. (185 km/h).  The minimum surface pressure was 961 mb.

Typhoon Krovanh remains in a very favorable environment.  It is over water with warm Sea Surface Temperatures and the upper level winds are light.  The absence of significant vertical wind shear has allowed upper level divergence to continue to pump away mass in all directions.  The structure of the inner core of Krovanh improved as it intensified and the typhoon now has a well developed eye surrounded by a nearly complete eyewall.  The favorable environment could allow Krovanh to intensify for another 24 to 36 hours.  When the typhoon begins to approach latitude 30°N, it will begin to be affected by the upper level westerly winds in the middle latitudes.  The increased vertical wind shear will begin to weaken Krovanh.

Typhoon Krovanh is moving around the western end of a subtropical ridge.  The ridge should steer Krovanh toward the northwest for another 24 hours.  When it reaches the western end of the ridge, the typhoon will start moving toward the north.  As the upper level westerly winds start to affect Krovanh, those winds will accelerate it toward the northeast.  On its anticipated track Krovanh could be approaching Iwo To in about 24 hours and it could be near Chichi Jima in about 36 hours.  Krovanh could be a strong typhoon when it passes those islands.

Tropical Storm Krovanh Organizing Quickly Near Northern Marianas

The circulation around Tropical Storm Krovanh is organizing quickly as it passes near the northern Marianas.  At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Krovanh was located at latitude 19.3°N and longitude 148.1°E which put it about 170 miles (275 km) east-northeast of Agrihan in the northern Mariana Islands.  Krovanh was moving toward the northwest at 11 m.p.h. (18 km/h).  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (105 km/h).  The minimum surface pressure was 995 mb.  A Tropical Storm Watch has been issued for Alamagan, Pagan and Agrihan in the northern Marianas.

The circulation near the center of Krovanh organized quickly on Tuesday.  A primary spiral rainband wrapped around the southern side of the center and an eyelike feature has appeared intermittently on visible satellite imagery.  Additional rainbands are developing around the circulation.  The thunderstorms near the core of the tropical storm are producing upper level outflow in all directions which is pumping out mass and is allowing the surface pressure to decrease.

Tropical Storm Krovanh is moving over water where the Sea Surface Temperature is near 30°C.  Upper levels winds are light and there is little vertical wind shear.  The environment is very favorable for further intensification and rapid intensification is likely.  Krovanh could become a typhoon within 24 hours and it could be a strong typhoon within several days.

A subtropical ridge located northeast of Krovanh is steering the tropical storm toward the northwest.  That general steering pattern is expected to continue for the next 48 hours.  After that time Krovanh will reach the western end of the subtropical ridge and it will turn toward the north.  On its anticipated track Krovanh will pass through the extreme northern Marianas on Wednesday and it be approaching Iwo To in about 48 hours.  Krovanh could be a strong typhoon at that time.

Tropical Storm Vamco Forms East of Vietnam

A large area of low pressure east of Vietnam developed enough organization on Sunday to be classified as Tropical Storm Vamco.  At 11:00 p.m. EDT on Sunday the center of Tropical Storm Vamco was located at latitude 14.8°N and longitude 110.0°E which put it about 160 miles (260 km) east-southeast of Da Nang, Vietnam.  Vamco was moving toward the west at 10 m.p.h. (16 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 1000 mb.

Although there is a large area of low pressure, the circulation around Tropical Storm Vamco is not well organized.  Most of the thunderstorms are located in a large rainband about 100 miles (160 km) from the center of circulation that wraps around the northern and western parts of the storm.  There are not many thunderstorms located near the center of the circulation.  Vamco is located over water where the Sea Surface Temperature is near 30°C.  However, an upper level ridge is generating northeasterly winds over the top of the storm and the vertical wind shear is inhibiting development.  Some intensification is possible in the short term, but the lack of a well formed inner core and proximity to land will limit strengthening.

A subtropical ridge north of Vamco is steering the tropical storm toward the west and that steering pattern is expected to continue.  On its anticipated track the center of Vamco will reach the central coast of Vietnam in about 18 hours.  The primary impacts will be locally heavy rainfall and the potential for flooding.

Tropical Storm Henri Forms East of Bermuda

An instrument on a satellite indicated that there could be surface winds to tropical storm force in an area of thunderstorms east of the center of Tropical Depression Eight and the National Hurricane Center designated the system as Tropical Storm Henri.  At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Henri was located latitude 31.3°N and longitude 60.7°W which put it about 250 miles (405 km) east-southeast of Bermuda.  Henri was moving toward the north at 5 m.p.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 1008 mb.

Henri is not a very well organized tropical storm.  An upper level low centered north of Bermuda is causing brisk southwesterly winds over the top of Henri.  The vertical wind shear is blowing the tops off of thunderstorms that start to form near the center of circulation.  As a result of the wind shear, the stronger thunderstorms are all located well to the east of the center of the tropical storm.  Henri is over warm Sea Surface Temperatures (SSTs) which are above normal in that part of the western Atlantic Ocean.  So, there is plenty of energy to support intensification.  However, as long as the upper level low creates significant vertical wind shear, intensification will be minimal.  It is possible that as Henri moves toward the north that the wind shear could decrease.  In that case Henri could intensify during the next day or two before it moves over cooler SSTs.

An upper level trough over the eastern U.S. should steer Henri toward the north during the next several day.  On its anticipated track, Henri could pass near Newfoundland during the weekend.  Henri could be in the process of transitioning from a tropical storm to an extratropical cyclone at that time, but it could still bring strong winds and rain to parts of extreme eastern Canada.

Linda Rapidly Intensifies Into a Major Hurricane

Hurricane Linda rapidly intensified on Tuesday and it now has a wind speed that qualifies it as a Category 3 Hurricane on the Saffir-Simpson Scale.  This makes Linda the fifth major hurricane in the Eastern North Pacific in 2015.  At 11:00 a.m. EDT on Tuesday the center of Hurricane Linda was located at latitude 21.3°N and longitude 113.9°W which put it about 280 miles (450 km) west-southwest of the southern tip of Baja California.  Linda was moving toward the north-northwest at 14 m.p.h. (22 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 956 mb.

Upper level winds over Linda decreased and the reduction in vertical wind shear allowed it to intensify rapidly during the past 12 hours.  A visible eye and symmetrical eyewall are evidence of a well organized inner core.  Thunderstorms near the center of circulation are generating upper level divergence in all directions which is pumping out mass and causing the pressure to decrease.  Linda could intensify for a few more hours, but it will start to move over much cooler Sea Surface Temperatures (SSTs) later today.  It will be unable to extract enough energy from the cooler water to maintain its intensity and Linda will start to weaken.  As Linda moves farther north, it will also start to encounter stronger upper level winds around the southern portion of an upper level trough near the west coast of the U.S.  Increased vertical wind shear in addition to cooler SSTs will speed up the rate at which Linda weakens.  Since Linda has a large circulation, it could take longer for it to spin down.

An upper level ridge over Mexico is steering Linda toward the north-northwest and that general motion is expected to continue as long as it maintains tall thunderstorms.  When Linda weakens to a tropical storm over cooler water, the circulation will not extend as high in the atmosphere.  After that time Linda will be steered more toward the west by winds lower in the atmosphere.  On its anticipated track Linda will move parallel to the coast of Baja California for several days before turning away from the coast later this week.

Tropical Storm Etau Develops and Heads Toward Japan

A center of circulation developed within a large area of thunderstorms a few hundred miles south of Japan and the system has been designated Tropical Storm Etau.  At 11:00 a.m. EDT on Monday the center of Tropical Storm Etau was located at latitude 25.3°N and longitude 138.5°E which put it about 720 miles (1160 km) south-southeast of Osaka, Japan.  Etau was moving toward the north at 11 m.p.h. (18 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 998 mb.

Although Tropical Storm Etau does have a low level center of circulation, most of the stronger thunderstorms are located north-northwest of the center.  Etau is moving over water where the Sea Surface Temperatures are warm enough to support intensification.  However, a large upper level trough west of Japan is producing southwesterly winds over the top of the tropical storm.  The circulation appears to be tilting toward the north with height because  of vertical wind shear.  Tilted tropical cyclones are unable to efficiently convert energy to wind speed and intensify.  Etau could intensify a little during the next 24 hours, but then it will run into much stronger upper level winds associated with the upper level trough.  Stronger vertical wind shear will cause Etau to begin to weaken before it reaches Japan.

A subtropical ridge east of Etau is steering it toward the north-northwest and that general motion is expected to continue for the next several days.  On its anticipated track Etau will approach the coast of Japan near Honshu and Shikoku.  Landfall somewhere between Nagoya and Kochi could occur in about 36 hours.  Etau’s biggest impact will be to increase rainfall as it moves inland.

Tropical Storm Linda Forms South of Baja California

A spiral band continued to wrap more tightly around the center of circulation inside a large low pressure system west of Mexico on Sunday and the National Hurricane Center designated the system as Tropical Storm Linda.  At 11:00 a.m. EDT on Sunday the center of Tropical Storm Linda was located at latitude 14.1°N and longitude 109.0°W which put it about 610 miles (980 km) south of the southern tip of Baja California.  Linda 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 1000 mb.

The circulation in Tropical Storm Linda is well organized.  There is one main spiral rainband and multiple outer rainbands.  Outside of the core of the circulation there are fewer thunderstorms east of the center, which could mean that some drier air is being pulled into that part of the storm.  Thunderstorms in the core are generating upper level divergence.  Linda is over water where the Sea Surface Temperatures (SSTs) are above 29°C.  An upper level trough near the west coast of the U.S. and an upper level ridge over northern Mexico are combining to create an outflow channel to the northeast, which is enhancing the flow of mass away from the tropical storm.  There is little vertical wind shear over the top of Linda and the environment is favorable for further intensification.  A period of rapid intensification is possible and Linda is likely to become a hurricane.  Eventually, when it moves farther north, Linda will move into an area of cooler SSTs and more vertical wind shear, which will cause it to weaken.

Linda appears to be moving a little more toward the west-northwest this afternoon.  The upper level ridge over northern Mexico is expected to steer it in a generally northwesterly direction during the next few days.  On its anticipated track, Linda would move west of Baja California during the middle of next week.

Tropical Storm Grace Forms Southwest of Cape Verde

Enough organization developed in the center of an area of low pressure that moved off the coast of Africa several days ago for the National Hurricane Center to classify it as Tropical Storm Grace.  At 5:00 p.m. EDT on Saturday the center of Tropical Storm Grace was located at latitude 12.6°N and longitude 26.4°W which put it about 285 miles (460 km) southwest of the Cape Verde Islands.  Grace was moving toward the west at 14 m.p.h. (22 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 1007 mb.

The area of low pressure that became Tropical Storm Grace had a large area of thunderstorms when it moved off the coast of West Africa.  A few thunderstorms developed closer to the center of circulation and there are signs that a couple of spiral bands could be forming near the core of Grace.  The strongest thunderstorms are occurring in the southwestern quadrant of the circulation.  Some of the thunderstorms appear to be getting taller, but the core of the circulation is still organizing.

Tropical Storm Grace is moving over water where the Sea Surface Temperature is near 29°C.  Although there are stronger upper level westerly winds north of the tropical storm, the vertical wind shear over Tropical Storm Grace is relatively modest.  It has a day or two for the core of the circulation to organize and to intensify.  When Grace moves farther west it could move into a region where there is drier air.  An upper level trough could produce more vertical wind shear when the tropical storm gets closer to the Caribbean Sea.

A subtropical ridge is steering Grace toward the west and that steering pattern is expected to continue for the next few days.  If Grace gets stronger and the convection taller, it would take a track a little farther to the north.  If it remains weaker and shallower, lower level winds will steer it more to the west.  On its anticipated track, Grace could approach the Lesser Antilles in five or six days.