Monthly Archives: August 2016

Tropical Storm Lester Forms West of Mexico

Tropical Storm Lester became the 12th named tropical storm to form over the Eastern North Pacific Ocean during 2016 on Thursday.  At 5:00 p.m. EDT on Thursday the center of Tropical Storm Lester was located at latitude 16.9°N and longitude 113.4°W which put it about 470 miles (760 km) south-southwest of the southern tip of Baja California.  Lester 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 1000 mb.

Tropical Storm Lester formed when a distinct center of circulation developed within a tropical wave.  The core of the tropical storm is still consolidating.  There are thunderstorms near the center of circulation and there are spiral bands rotating around the core of Tropical Storm Lester.  The thunderstorms near the center are generating upper level divergence which is pumping away may to the south of the tropical storm.  There are hints of the possible formation of an eye on some satellite images.

Tropical Storm Lester is moving through an environment that is generally favorable for intensification.  It is moving over water where the Sea Surface Temperature is around 30°C.  An upper level ridge northwest of Lester is generating northerly winds which are blowing across the top of the tropical storm.  The northerly winds are producing some vertical wind shear, but the shear is only slowing the intensification process.  Tropical Storm Lester is expected to continue to intensify and it could become a hurricane.

A subtropical ridge is steering Tropical Storm Lester toward the west-northwest and that general motion is expected to continue.  On its anticipated track Tropical Storm Lester will move farther away from Mexico and it currently poses no threat to land.

Lionrock Becomes a Typhoon East of Okinawa

Tropical Storm Lionrock intensified into a typhoon east of Okinawa on Tuesday.  At 8:00 p.m. EDT on Tuesday the center of Typhoon Lionrock was located at latitude 25.3°N and longitude 132.8°E which put it about 340 miles (550 km) east-southeast of Okinawa.  Lionrock was moving toward the south-southwest at 11 m.p.h. (17 km/h).  The maximum sustained wind speed was 80 m.p.h. (130 km/h) and there were wind gusts to 100 m.p.h. (160 km/h).  The minimum surface pressure was 965 mb.

Lionrock is a fairly small typhoon.  Winds to tropical storm force only extend out about 150 miles (240 km) from the center.  The circulation of Typhoon Lionrock is very well organized.  A small distinct eye is visible on satellite imagery.  The eye is surrounded by a ring of strong thunderstorms.  Additional spiral rainbands are rotating around the core of Lionrock.  The thunderstorms around the eye are generating upper level divergence which is pumping out mass in all directions.

Typhoon Lionrock is in an environment that is favorable for intensification.  It is moving over water where the Sea Surface Temperature is near 30.5°C.  The upper level winds are weak and there is little vertical wind shear.  A small typhoon like Lionrock can intensify very quickly and it appears to be doing so.

An upper level ridge over China is steering Typhoon Lionrock slowly toward the south-southwest and that general motion is expected to continue for another day or two.  Lionrock could move into an area where the steering winds are weak and it could stall for a period of time.  Eventually, an upper level trough is expected to approach the area from the west and begin to pull Lionrock toward the north.

Tropical Storm Gaston Forms Southwest of the Cape Verde Islands

A center of circulation quickly organized within a tropical wave on Monday night and the National Hurricane Center designated the system as Tropical Storm Gaston.  At 11:00 p.m. EDT on Monday the center of Tropical Storm Gaston was located at latitude 12.6°N and longitude 30.7°W which put it about 450 miles (725 km) west-southwest of the Cape Verde Islands.  Gaston was moving toward the west-northwest at 18 m.p.h. (30 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 1005 mb.

The circulation consolidated rapidly around the center of Tropical Storm Gaston on Monday.  Several spiral bands of thunderstorms formed close to the center and additional bands formed farther from the center.  The thunderstorms near the center began to generate upper level divergence, which pumped mass away from the center.

Tropical Storm Gaston is moving through an environment that is favorable for intensification.  It is over water where the Sea Surface Temperature is near 28°C.  The upper level winds are light and there is little vertical wind shear.  Gaston is likely continue to intensify steadily during the next several days and it is expected to become a hurricane.  Once a tightly organized core consolidates completely, Gaston could undergo a period of more rapid intensification.

A subtropical ridge is steering Tropical Storm Gaston toward the west-northwest and that general motion is expected to continue for a day or so.  The ridge is expected to weaken northwest of Gaston, and the tropical storm is expected to turn more toward the north during the middle of the week.  Gaston could be moving out into the Central Atlantic Ocean by the end of the week.

Typhoon Mindulle Nearing Japan

Typhoon Mindulle moved steadily toward the coast of Japan on Sunday.  At 2:00 p.m. EDT on Sunday the center of Typhoon Mindulle was located at latitude 32.9°N and longitude 139.4°E which put it about 185 miles (305 km) south of Tokyo, Japan.  Mindulle was moving toward the north at 19 m.p.h. (31 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were wind gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 975 mb.

The circulation of Typhoon is reasonably well organized.  A primary rainband wraps most of the way around the northern and eastern sides of the center of circulation.  There is evidence of a partial eyewall north of the center.  Additional bands of thunderstorms are occurring in the northern half of the circulation.  The thunderstorms near the core of Mindulle are generating upper level divergence which is pumping away mass to the east of the typhoon.  However, there are fewer thunderstorms west of the center of circulation which may indicate the presence of dry air in that area.

Typhoon Mindulle is moving through an environment that is only marginal for further intensification.  It is currently moving over water where the Sea Surface Temperature is near 29°C, but Mindulle will move over cooler water when it approaches the coast of Japan.  An upper level trough located to the west of Japan is generating southwesterly winds which are blowing across the top of Mindulle.  The moderate vertical wind shear is preventing upper level divergence to the west of the typhoon and the shear may also be partially responsible for the asymmetric distribution of thunderstorms.  It is also possible that Mindulle is pulling in some drier air located northwest of the typhoon.

The upper level trough is steering Mindulle toward the north and that general motion is expected to continue.  On its anticipated track the center of Typhoon Mindulle will reach the coast near Tokyo in 10-12 hours.  Heavy rain in some of the bands of thunderstorms north of the center could reach the coast at any time.  Since Mindulle is a typhoon, it is capable of causing minor wind damage.  A greater risk is the potential for locally heavy rainfall and flash flooding.

Tropical Storms Lionrock and Kompasu Spin Up Near Japan

A large cyclonic atmospheric gyre near Japan spun up two more tropical storms at the end of the week.  The Japan Meteorological Agency named two smaller circulations within the larger gyre Tropical Storm Lionrock and Tropical Storm Kompasu.

At 2:00 p.m. EDT on Saturday the center of Tropical Storm Kompasu was located at latitude 37.8°N and longitude 142.3°E which put it about 75 miles (120 km) east of Sendai, Japan.  Kompasu was moving toward the northwest at 26 m.p.h. (42 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 996 mb.

At 2:00 p.m. EDT on Saturday the center of Tropical Storm Lionrock was located at latitude 30.6°N and longitude 135.7°E which put it about 530 miles (860 km) east-northeast of Okinawa.  Lionrock was moving toward the west-southwest 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 994 mb.

Tropical Storm Kompasu is located farther north and it is beginning to make a transition into an extratropical cyclone.  Kompasu is moving over water where the Sea Surface Temperature (SST) is near 26°C, but it is moving rapidly toward cooler SSTs.  Most of the thunderstorms are in a single primary rainband that wraps around the southern part of the circulation.  An upper level trough west of Japan is pulling southwesterly winds across the top of Tropical Storm Kompasu and the vertical wind shear is increasing.

The upper level trough is expected to turn Tropical Storm Kompasu toward the northeast.  On its anticipated track Tropical Storm Kompasu will move across Hokkaido in about 18 hours.  It will bring locally heavy rain and some wind.

Tropical Storm Lionrock is more well organized.  Several spiral bands of thunderstorms are wrapping around the southern and east sides of the center of circulation.  There is drier air in the western portion of the circulation and there are few thunderstorms in that part of Lionrock.  The thunderstorms east of the center are generating upper level divergence that is pumping mass toward the northeast away from core of Tropical Storm Lionrock.

Tropical Storm Lionrock is in an environment that is somewhat favorable for additional intensification.  It is moving over water where the SST is near 30°C.  The upper level trough west of Japan is generating some vertical wind shear.  The drier air in the western part of the circulation will also inhibit intensification, but Lionrock could gradually get better organized.  Upper level outflow from stronger Tropical Storm Mindulle, which is southwest of Lionrock, could produce enough vertical wind shear to weaken Lionrock at times.

The large atmospheric gyre is steering Tropical Storm Lionrock toward the west-southwest.  Lionrock could be pulled more toward the south as the larger, stronger Tropical Storm Mindulle passes east of it.  Tropical Storm Lionrock is expected to remain south of Japan during the next several days.  An alternative scenario would be for Tropical Storm Mindulle to intensify into a typhoon and grow large enough to absorb the circulation of Lionrock.

Tropical Storm Mindulle Forms Northwest of Guam

A smaller center of circulation consolidated within a much larger cyclonic gyre that extends from the Marianas north to Japan and west to China and the system has been designated Tropical Storm Mindulle.  At 11:00 a.m. EDT on Friday the center of Tropical Storm Mindulle was located at latitude 19.5°N and longitude 141.0°E which put it about 410 miles (655 km) south of Iwo To.  Mindule was moving toward the north-northwest at 11 m.p.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 992 mb.

The circulation around Tropical Storm Mindulle is still organizing.  A primary rainband is wrapping about three quarters of the way around the broad center of circulation.  There are few thunderstorms close to the core of tropical storm.  Scattered thunderstorms are forming in broken bands outside the primary rainband.  The thunderstorms in the primary rainband are generating some upper level divergence which is mainly pumping mass to the southwest of the center of circulation.

Tropical Storm Mindulle is in an environment that is favorable for slow intensification.  It is moving over water where the Sea Surface Temperature is near 31°C.  The upper level pattern near Mindulle is quite complex with a number of different features.  A narrow upper level ridge is just north of Mindulle and it is producing northeasterly winds that are blowing across the top of the tropical storm.  The northeasterly winds are contributing to the fact that most of the thunderstorms are west of the center of circulation and they are causing moderate vertical wind shear.  The vertical wind shear is inhibiting intensification.  Tropical Storm Mindulle is expected to extract enough energy from the ocean to intensify.  However, intensification will be slow while the core of the circulation organizes.

Tropical Storm Mindule is moving around the eastern portion of the large cyclonic gyre mentioned above.  That gyre is steering Mindulle toward the north-northwest and a general motion toward the north is expected to continue.  On its anticipated track Tropical Storm Mindulle could pass near Iwo To in about 24 hours.  Mindulle could be near Tokyo, Japan in about three days.

Tropical Storm Kay Forms South of Baja California

A distinct center of circulation consolidated within a cluster of thunderstorms south of Baja California and the National Hurricane Center designated the system as Tropical Storm Kay.  At 5:00 a.m. EDT on Friday the center of Tropical Storm Kay was located at latitude 18.4°N and longitude 110.9°W which put it about 315 miles (510 km) south-southwest of the southern tip of Baja California.  Kay 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 1005 mb.

The circulation of Tropical Storm Kay is only moderately well organized.  Most of the stronger thunderstorms are occurring in a band that wraps around the western side of the circulation.  There are also scattered thunderstorms in broken bands around the tropical storm, but much of the convection is occurring in the western half of Kay.  The thunderstorms in the primary rainband are generating some upper level divergence which is moving air to the west of the Tropical Storm Kay.

Tropical Storm Kay is moving through an environment that is marginally favorable for intensification in the short term.  Kay is moving over water where the Sea Surface Temperature (SST) is near 29°C.  An upper level ridge to the north of Kay is generating northeasterly winds which are blowing across the top of the tropical storm.  The moderate vertical wind shear is inhibiting intensification and it is also contributing to the asymmetrical distribution of thunderstorms.  The effect of the warm SSTs could allow for some additional intensification during the next 24 hours.  Tropical Storm Kay will be moving over cooler SSTs during the weekend and the effect of the effect of the cooler water with less energy will weaken the storm.

Tropical Storm Kay is moving around the western end of a subtropical ridge and that is steering the storm toward the northwest.  That general motion is expected to continue for another 24 to 48 hours.  When Tropical Storm Kay moves over cooler SSTs, the thunderstorms will weaken and the circulation will become shallower.  The shallower circulation will be steered by the winds closer to the surface, which are expected to turn Tropical Storm Kay more toward the west in a couple of days.  On its anticipated track Tropical Storm Kay will pass west of Baja California.

Tropical Storm Dianmu Forms Near Hainan Island

A center of circulation developed within a larger cyclonic rotation associated with the monsoon near Hainan Island and the Japan Meteorological Agency classified the system as Tropical Storm Dianmu.  At 5:00 a.m. EDT on Thursday the center of Tropical Storm Dianmu was located at latitude 20.5°N and longitude 109.7°E which put it about 265 miles (430 km) east of Hanoi, Vietnam.  Dianmu 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 985 mb.

The circulation of Tropical Storm Dianmu consists of a smaller counterclockwise rotation inside a much larger cyclonic flow associated with the monsoonal circulation.  Thunderstorms clustered around the western and southern portion of the smaller counterclockwise rotation and a distinct inner core developed that is separate from the broader center of the monsoonal gyre.  Additional spiral bands formed outside the core.  The thunderstorms are generating upper level divergence, primarily to the south and west of Tropical Storm Diamnu.

Tropical Storm Dianmu is moving through an environment that is favorable for additional strengthening.  It is moving over water where the Sea Surface Temperature is near 31°C.  An upper level ridge centered over China is producing easterly winds which are blowing across the top of Tropical Storm Dianmu.  Those winds are causing moderate vertical wind shear, which is slowing the rate of intensification of the tropical storm.  The proximity of Dianmu to the coast is also slowing the rate of intensification.  Tropical Storm Dianmu has 12 to 18 hours to intensify before it moves over land.

The upper level ridge over China is steering Tropical Storm Dianmu toward the west and that general motion is expected to continue.  On its anticipated track the center of Tropical Storm Dianmu could reach the coast of Vietnam in 12 to 18 hours.  Dianmu could cause some minimal wind damage and storm surge, but heavy rain will be the greatest threat.  Tropical Storm Dianmu could cause flash flooding when it moves inland over Southeast Asia.

Tropical Depression Six Intensifies Into Tropical Storm Fiona

Tropical Depression Six intensified on Wednesday and the National Hurricane Center named it Tropical Storm Fiona.  At 5:00 p.m. EDT on Wednesday the center of Tropical Storm Fiona was located at latitude 15.1°N and longitude 37.8°W which put it about 1545 miles (2490 km) east of the Leeward Islands.  Fiona was moving toward the northwest at 16 m.p.h. (26 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 Fiona has a small circulation and winds to tropical storm force only extend out about 25 miles (40 km) from the center circulation.  Most of the thunderstorms are occurring close to the center of circulation.  Those thunderstorms are generating some upper level divergence, but it does not extend very far from the core of Tropical Storm Fiona.  There are bands of lower clouds and showers rotating around the core of Fiona.

Tropical Storm Fiona is moving through an environment that is mostly favorable for intensification.  It is moving over water where the Sea Surface Temperature is near 27°C.  An upper level ridge north of Fiona is generating northeasterly winds which are blowing across the top of the tropical storm.  Those winds are causing some vertical wind shear, but it should only inhibit, but not stop, intensification.  There is drier air northwest of Fiona and that is the main negative factor in the environment.  If the drier air gets pulled into the core of Tropical Storm Fiona, it will reduce the supply of energy and weaken Fiona.  Since the core of Fiona is so small, the tropical storm could intensify or weaken very quickly as the environmental conditions change.

The subtropical high that extends from Africa across the Atlantic Ocean is splitting into an eastern ridge and a western ridge.  Tropical Storm Fiona is moving toward the weakness where the split is occurring.  This is producing a motion toward the northwest and that general motion is expected to continue during the next several days.  On its anticipated track Tropical Storm Fiona could be northeast of the Leeward Islands in a few days.

Tropical Depression Six Forms Over Eastern Atlantic

A center of circulation developed within a tropical wave designated as Invest 98L on Tuesday and the National Hurricane Center classified the system as Tropical Depression Six.  At 11:00 p.m. EDT on Tuesday the center of Tropical Depression Six was located at latitude 12.6°N and longitude 34.1°W which put it about 1800 miles (2900 km) east of the Leeward Islands.  The 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. (70 km/h).  The minimum surface pressure was 1008 mb.

The circulation of Tropical Depression Six is still organizing.  A center of circulation exists near the surface and thunderstorms are developing near the center.  Several partial spiral bands are beginning to form.  The thunderstorms near the center are generating a small region of upper level divergence, but the divergence is occurring mainly to the southwest of the depression.

Tropical Depression Six is moving through an environment that favors intensification.  It is moving over water where the Sea Surface Temperature is near 27°C.  An upper level ridge to the north is causing northeasterly winds to blow across the top of the depression.  There is some vertical wind shear, but the shear will only slow the rate of intensification.  The shear is not strong enough to prevent intensification and Tropical Depression Six is expected to become a tropical storm during the next day or two.

The subtropical ridge over Africa and the Atlantic Ocean is splitting into two parts and Tropical Depression Six is moving toward the northwest into the split that is developing.  The depression is expected to continue to move toward the northwest in the short term.  The longer term motion will depend on how strong Tropical Depression Six becomes.  If it intensifies more and develops a taller circulation, then the depression will be steered by the winds higher in the atmosphere.  The winds at those levels are more likely to carry it into the central Atlantic Ocean.  However, if vertical wind shear weakens the depression and the circulation is shallower, then the winds in the lower levels of the atmosphere could carry the depression farther to the west.  In either case Tropical Depression Six is no immediate threat to any land area.