Category Archives: Tropical Cyclones

Information about tropical cyclones

Karina, Lowell and Marie

The atmosphere over the tropical Eastern North Pacific Ocean remains active with two hurricanes and a tropical storm.  Karina re-intensified into a hurricane about 1400 miles east of Hawaii.  It is moving slowly to the northeast as it is drawn into the large circulation around tropical storm Lowell.  Although the atmospheric conditions are allowing it to maintain hurricane force winds at the moment, it will encounter less favorable conditions as it moves farther north.

Tropical Storm Lowell is slowly spinning down about 1000 miles west of Baja California.  Lowell is moving slowly northwestward over cooler Sea Surface Temperatures (SSTs).  The SSTs are cool enough that Lowell is only generating lower clouds and it has not produced any deep thunderstorms in recent hours.  Lowell could be reclassified as a non-tropical low later today or tomorrow.  Lowell has a large circulation and it will take it a few days to spin down completely.

Hurricane Marie is intensifying rapidly about 330 miles south-southwest of Manzanillo, Mexico.  It currently has a maximum sustained wind speed of 85 m.p.h. and it could become a major hurricane during the next day or two.  Marie has a large well organized circulation and upper level divergence is well established over it.  It is expected to move northwestward parallel to the west coast of Mexico.  Marie is the 13th named tropical cyclone and 8th hurricane of the Eastern North Pacific 2014 season.

Update on Invest 96L

A tropical disturbance approaching the Lesser Antilles was designated Invest 96L by the National Hurricane Center (NHC).  The disturbance appears to consist of a tropical wave, a broad surface low centered east of Guadaloupe and a small cyclonic meso-vortex rotating around the northeastern portion of the broader low pressure system.  The overall system is moving toward the west-northwest at 21 m.p.h.  There appears to be a broad area of light winds within the surface low and stronger winds on the north side of the small meso-vortex.  A reconnaissance aircraft did find winds to tropical storm force on the north side of the system, but it also reported that the overall circulation was poorly defined.

This disturbance has a complicated origin which is linked to its slow development.  The disturbance originally consisted of two tropical waves moving north of a broad but weak low pressure system located within the Intertropical Convergence Zone/monsoon trough.  The complex structure inhibited the development of a dominant center of circulation and several clusters of thunderstorms have produced small meso-vortices like the one mentioned previously.  It appears that there has been a slight increase in organization today as the broad area of low pressures appears to have a more symmetrical shape.  It is unclear if an upper low to the northwest of the system is creating wind shear over the top of it.

NHC is giving a 70% chance that a tropical cyclone will form out of this system within the next five days.  As broad low pressure system moves west-northwest it will affect the weather over the northeastern Caribbean Sea during the next several days.  Another reconnaissance aircraft is scheduled to investigate the disturbance tomorrow afternoon, if necessary.

 

Possible Tropical Development

For the first time this hurricane season the Global System Forecast (GFS) Model is suggesting a classical development of a tropical cyclone east of the Lesser Antilles might occur and that resulting storm could effect the U.S.  A tropical wave is about 600 miles east of the Lesser Antilles and there may be a low pressure center near latitude 10°N and longitude 50°W.  Thunderstorm activity has increased with this system today as it moves westward.

The 0600 UTC run of the GFS model developed a tropical cyclone from this wave and moved it through the Caribbean Sea and into the Gulf of Mexico near Texas by a week from Friday.  The following (1200 UTC) run also developed a tropical cyclone and moved it into the northern Gulf of Mexico by a week from Wednesday evening.  At this time it is prudent to ask if these runs represent model false alarms or a possible depiction of future reality.  If the development of a tropical cyclone does occur, then it may be that a hurricane could approach the coast of the U.S. during the second half of next week.  The first indication that the GFS forecast might verify would be the development of tropical depression east of the Lesser Antilles.

This far out in advance the uncertainty of a track or intensity forecast is very high.  If there was a cone of uncertainty for the track, it might extend from Cancun to Cape Hatteras.  If a center of low pressure organizes, then the model guidance will improve and the uncertainty will decrease.

People along the coast of the U.S. should be aware of this system and maintain a cautious vigilance until we see if it does develop,

Tropical Storms Karina and Lowell and the Fujiwhara Effect

I am sometimes asked what happens when two tropical cyclones get close to each other.  The answer depends on the relative size and intensity of the two systems and how close they come to each other.  The Fujiwhara Effect is the name given to the tracks taken by the two vorticies.  If the two tropical cyclones are of nearly equal size and intensity, then they tend to move cyclonically around a center of rotation that is roughly half way between them.  If one cyclone is much bigger and stronger, then the center of rotation is shifted toward the bigger and stronger cyclone.

Tropical Storm Lowell has a large circulation and a maximum sustained wind speed of around 50 m.p.h.  Tropical Storm Karina is located about 700 miles to the west-southwest of Lowell.  Karina has a much smaller circulation and it also has a maximum sustained wind speed of 50 m.p.h.  Some of the models are forecasting that the two tropical storms will rotate around a point closer to Lowell than to Karina (i.e. the Fujiwara Effect).  This would result in Lowell moving general west-northwest and pass to the north of Karina.  The larger circulation of Lowell could also pull Karina back toward the east-northeast as Karina passes south of Lowell.  It is also possible that the circulation of Lowell could be so big that it captures Karina and Karina eventually gets absorbed by Lowell.

 

Three Tropical Waves

There are three notable tropical waves spread across the Atlantic and Caribbean this morning.  The first wave is over the eastern Caribbean Sea.  Thunderstorm activity has been gradually increasing with this wave and there may be an 850 mb vorticity center near latitude 12°N and longitude 62°W.  The wave extends northward to just east of Puerto Rico.  The wave is moving westward.  The models are not forecasting development of a tropical cyclone out of this wave at this time, but it may bear watching if the convection continues to increase.

A second tropical wave is located midway between Africa and the Lesser Antilles.  A low pressure system is located in the wave near latitude 12°N and longitude 36°W.  Cyclonic turning of the clouds is evident in satellite loops.  Drier air in the northern portion of the wave is limiting convective activity to the southern half of the cyclonic circulation.  Some runs of the GFS indicate modest development of the low pressure system as it moves westward.  In other GFS runs the low weakens before it reaches the Lesser Antilles.

A third tropical wave is located half way between Africa and the Cape Verde Islands.  A low pressure system is located in the wave near latitude 15°N and longitude 20°W.  Convection was impressive last night when the low first emerged from Africa and moved over the Atlantic.  However, strong easterly winds in the upper levels sheared the top off of this system and only a low level cyclonic circulation remains.   Earlier model runs indicated possible development of a tropical cyclone out of this wave, but more recent runs indicate that the upper level shear will continue and prevent development.

 

The Atlantic remains quiet

Tropical waves continue to move off Africa and weaken over the Atlantic Ocean.  A tropical wave about a thousand miles east of the Lesser Antilles continues to move westward with little convection.  Earlier in the week some models runs were suggesting that the wave might form into a tropical cyclone, but the models are no longer indicating that development will occur.

Julio becomes a hurricane again

An eye developed in Julio and it has been upgraded to hurricane status.  Even though Julio is located 600 miles north of Hawaii, it is over Sea Surface Temperatures (SSTs) that are warm enough to support a hurricane.  The upper level winds around Julio are light enough to allow for Julio to maintain a warm core.  Eventually, wind shear should increase and cooler SSTs will likely weaken Julio back to a tropical storm.

A new tropical depression has formed west of Mexico.  Tropical Depression Eleven-E (TD11E) is about 385 miles west-southwest of Manzanillo, Mexico and about 400 miles south of the southern tip of Baja, California.  it is moving toward the west-northwest at 16 m.p.h.  It is expected to intensify and if it becomes a tropical storm its name will be Karina.  Some numerical models are showing that it could eventually move in the general direction of Hawaii.