Monthly Archives: August 2014

Category 5 Hurricane Marie

Hurricane Marie continued to intensify rapidly as it moved westward away from Mexico.  It now has maximum sustained winds to 160 m.p.h. which makes it a Category 5 hurricane on the Saffir-Simpson Scale.  Marie is the first hurricane to reach Category 5 intensity over the Eastern North Pacific since Hurricane Celia in 2010.  Marie is a large hurricane and it is approximately half the size of Hurricane Sandy, but Marie is a symmetrical storm.  Hurricane force winds extend out 35-60 miles in all quadrants of Marie.  Marie is in a favorable environment with warm Sea Surface Temperatures and little vertical wind shear.  It could strengthen a little more or it may have attained its peak intensity.  Some satellite imagery suggests that a second eyewall may be forming and an eyewall replacement cycle would initially produce weakening followed possibly by fluctuations in intensity.

The Hurricane Intensity Index (HII) for Marie is 35.0.  The Hurricane Size Index (HSI) is 21.5.  The Hurricane Wind Intensity Size Index (HWISI) is 56.5.

TD4 becomes Tropical Storm Cristobal

Reconnaissance aircraft found that the maximum sustained wind speed in Tropical Depression Four has increased to 45 m.p.h. and it has been upgraded to Tropical Storm Cristobal.  At 8:00 a.m. EDT the center of Cristobal was located at latitude 23.0°N and longitude 73.0°W which put it about 135 miles east-southeast of Long Island in the Bahamas and about 480 miles east-southeast of Miami, Florida.  Cristobal was moving toward the northwest at 9 m.p.h.  The minimum surface pressure was 1002 mb.  Tropical Storm Warnings remain in effect for the Southeastern and Central Bahamas and the Turks and Caicos.

Upper level winds from the northwest appear to be creating wind shear over Cristobal.  Most of the convection is occurring east and south of the center.

Tropical Depression Four

A reconnaissance aircraft found westerly winds in the southeastern side of a low pressure system over the Southeastern Bahamas and was able to close off a center of circulation.  As a result the National Hurricane Center classified the low as Tropical Depression Four (TD4).  At 5:00 p.m. EDT on Saturday the center of TD4 was located at latitude 21.8°N and longitude 72.3°W which put it about 75 miles northeast of Great Inagua Island in the Bahamas and about 560 miles east-southeast of Miami, Florida.  TD4 was moving toward the northwest at 12 m.p.h.  The maximum sustained wind speed was 35 m.p.h. and the minimum surface pressure was 1005 mb.

Tropical Storm Warnings have been issued for the Southeastern Bahamas including The Acklins, Crooked Island, Long Cay, The Inaguas, Mayaguana and the Ragged Islands as well as The Turks and Caicos Islands and the Central Bahamas including Cat Island, The Exumas, Long Island, Rum Cay and San Salvador.

A small upper low north of Cuba is causing some wind shear over the western portion of TD4.  On the other hand the Sea Surface Temperatures around The Bahamas are very warm and TD4 is very likely to intensify into Tropical Storm Cristobal and eventually into a hurricane.  Since the center has just formed the motion and future track are still highly uncertain, although a general motion toward the southeastern U.S. seems likely.

Invest 96L

The circulation around the tropical disturbance designated 96L has been disrupted by the mountains on Hispaniola.  There a appears to be a broad low level center near the northern coast of Haiti.  There are several smaller vorticies rotating around within the broader area of low pressure.  The strongest winds are occurring north and east of the center and several reconnaissance flights found winds to tropical storm force north of the center.  The broad center appears to be moving toward the west-northwest at 10-15 m.p.h.   The area of low pressure has produced heavy rain on some of the islands of the northern Caribbean Sea.

It is still possible that 96L could organize into a tropical cyclone as it moves away from Hispaniola.  Once it gets away from the mountains, it will be easier for the flow to consolidate around one primary circulation center.  The Sea Surface Temperatures (SSTs) are very warm around the Bahamas and the upper level winds are not too strong.

There is a large amount of uncertainty about the future track of this system and that will continue until a well defined center of circulation exists.  It appears that the low has been initialized too far to the northeast in some runs of numerical models and that has produced some forecast tracks that are also too far north and east.  It is still possible that this system could head in the general direction of the southeastern U.S.

Development will possibly be slow to occur until the system becomes better organized.  Tropical cyclones can intensify rapidly over the Bahamas and people would be wise to monitor future developments with 96L.

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.