Monthly Archives: September 2015

Tropical Storm Dujuan Intensifying Southeast of Okinawa

After several days where vertical wind shear pushed most of the thunderstorms west of the core of the circulation, Tropical Storm Dujuan began to intensify on Wednesday.  At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Dujuan was located at latitude 18.9°N and longitude 132.7°E which put it about 620 miles (1000 km) southeast of Okinawa.  Dujuan was moving toward the west-northwest at 10 m.p.h. (16 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 988 mb.

The circulation near the core of Tropical Storm Dujuan is showing more organization.  Thunderstorms are developing closer to the center of circulation, although most of the stronger storms are still south and southwest of the center.  The distribution of thunderstorms is an indication that an upper level ridge west of Dujuan is still generating northeasterly winds over the top of the tropical storm.  Some of the storms closer to the center of circulation are starting to generate upper level divergence.

Dujuan is over water where the Sea Surface Temperatures are near 30°C.  Intensification is likely but vertical wind shear could limit the rate of intensification in the short term.  The wind shear is likely to decrease in a day or two as Dujuan moves into an area where the upper level winds are lighter.  Dujuan could become a typhoon within 24 to 36 hours and it could reach the equivalent of a major hurricane during the weekend.

Tropical Storm Dujuan is being steered toward the west-northwest by a subtropical ridge located to its northeast,  That general steering patter is expected to continue for another 24 to 36 hours.  At that time Dujuan will be between the ridge to its east and another upper level ridge to its west, and it could turn toward the northwest for a day or so.  The western ridge is expected to build north of Dujuan and turn it more toward the west in three or four days.  On its anticipated track Dujuan could approach the southern islands of Japan in three or four days.  It could be near Taiwan in five days.  Dujuan could be a strong typhoon by that time.

Tropical Depression 16E Could Bring Heavy Rain to Southwest U.S.

A center of circulation organized within a cluster of thunderstorms west of Baja California on Sunday and the system was designated Tropical Depression Sixteen-E.  At 5:00 p.m. EDT on Sunday the center of Tropical Depression Sixteen-E (TD16E) was located at latitude 25.0°N and longitude 113.7°W which put it about 90 miles (145 km) west of Cabo San Lazaro, Mexico.  TD16E was moving toward the north-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. (70 km/h).  The minimum surface pressure was 1003 mb.

Tropical Depression 16E has only a few hours before it will move over the central part of Baja California.  Although it is over water where the Sea Surface Temperature is near 27°C little, if any, intensification is expected.  When TD16E crosses Baja California, the terrain and increased vertical wind shear are likely to blow the upper portion of the circulation northward faster than the lower portion of the circulation.  The high clouds could reach parts of the southwestern U.S. within 24 hours.  Moving over mountains will disrupt the lower part of the circulation, but the rotation in the middle levels could persist for several days as it moves northward.

An upper level ridge centered over Texas and an upper level low west of Baja California are combining to steer TD16E northward and that general motion should continue for the next several days.  On its anticipated track TD16E could reach the coast of Baja California near Punta Abreojos in about 12 hours.  It could then move across Baja and the Gulf of California and make a second landfall on the coast west of Hermosillo on Monday morning.  TD16E or its remnants could be approaching southern Arizona later on Monday.  Convection and a flow of moisture associated with TD16E could produce locally heavy rainfall when it is forced to rise of mountains.  It could cause flooding in parts of Baja California, northwestern Mexico and the southwestern U.S.

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.