Category Archives: Tropical Cyclones

Information about tropical cyclones

Hurricane Norbert a little stronger

An Air Force Reserve Hurricane Hunter aircraft found that Hurricane Norbert was little stronger than was estimated based on satellite imagery.  At 2:00 p.m. EDT on Thursday the center of Hurricane Norbert was located at latitude 20.8°N and longitude 110.6°W which put it about 150 miles south-southwest of the southern tip of Baja California.  Norbert has been moving somewhat erratically, but the estimated motion was toward the northwest at 7 m.p.h.  The aircraft found that the maximum sustained wind speed was 90 m.p.h. and the minimum surface pressure was 970 mb.

Norbert is expected to move generally toward the northwest during the next several days and to move roughly parallel to the west coast of Baja California.  Although the center is expected to remain offshore, winds to tropical storm force may reach parts of Baja California.  For that reason a Tropical Storm Warning has been issued for the portion of the coast that extends from La Paz southward to the southern tip of Baja California and then northward to Cabo San Lazaro, Mexico.  Tropical Storm Watches have been issued for the portions of the coast from La Paz northward to San Evaristo and from Cabo San Lazaro northward to Puerto San Andresito.

The eye appears to be becoming more evident on visible satellite images.  There is some upper level shear from the northeast, but some additional intensification is possible during the next 24 hours.  When Norbert begins to move west of Baja California it will move over a very strong gradient of Sea Surface Temperatures (SSTs) toward colder water.  It will move from SSTs near 30°C to SSTs near 23°C.  The colder SSTs will greatly reduce the energy available to drive the circulation.  In addition, the atmosphere tends to be quite stable over the cooler SSTs, which will further inhibit convection and help to spin down the circulation.

Where the wind direction creates a flow up the slopes of mountains, locally heavy rainfall could occur and the potential for flooding exists in some locations.  Southerly flow around the eastern side of Norbert’s weakening circulation could transport moisture into portions of the southwestern U.S.

 

Tropical Storm Norbert Intensifying

Tropical Storm Norbert is becoming more organized as it moves in the general direction of Baja California.  At 8:00 a.m. EDT the center of Norbert was located at latitude 19.7°N and longitude 108.3°W which put it about 245 miles south-southeast of the southern tip of Baja California.  Norbert was moving toward the west-northwest at 8 m.p.h.  The maximum sustained wind speed was 60 m.p.h. and the minimum surface pressure was 999 mb.  The Tropical Storm Watch for the portion of the coast from La Paz to Sante Fe, Mexico has been upgraded to a Tropical Storm Warning.  A Tropical Storm Watch has been issued for the portion of the coast from Sante Fe northward to Cabo San Lazaro.

Norbert is over warm Sea Surface Temperatures (SSTs) and the upper level wind shear appears to be decreasing.  Some satellite imagery is indicating that an eye could be forming in the mid-levels of the circulation.  Further intensification is likely and a period of more rapid intensification is possible.  Norbert could become a hurricane before it reaches cooler SSTs west of Baja California.

 

Tropical Storm Norbert Forms

A center of circulation developed within a trough of low pressure southwest of Manzanillo, Mexico and the National Hurricane Center classified it as Tropical Storm Norbert.  At 5:00 p.m. EDT the center of Tropical Storm Norbert was located at latitude 18.5°N and longitude 106.5°W which put it about 150 miles west-southwest of Manzanillo and about 375 miles south of the southern tip of Baja California.  Norbert was moving toward the north at 9 m.p.h.  The maximum sustained wind speed was 40 m.p.h. and the minimum surface pressure was 1004 mb.  The government of Mexico has issued a Tropical Storm Watch for Baja California Sur from La Paz, around the southern tip of Baja California to Santa Fe.

Although there is some northeasterly shear over Norbert, the tropical storm is expected to intensify and at least one numerical model is predicting that it will become a hurricane.  Since Norbert is still in the organization stage, the track forecast has a higher than normal degree of uncertainty.  Many models are predicting that Norbert will move toward Baja California, but turn west-northwest before the storm reaches the coast.  The government of Mexico issued a Tropical Storm Watch for a portion in the coast in case Norbert moves closer to the coast than is currently expected.

 

TD 5 becomes Tropical Storm Dolly

Tropical Depression Five intensified into Tropical Storm Dolly during the overnight hours.  An Air Force Reserve Hurricane Hunter reconnaissance aircraft found that the maximum sustained wind speeds around Tropical Depression Five had increased to tropical storm force and the National Hurricane Center upgraded the system to Tropical Storm Dolly.  The plane also found that a new center of circulation had developed farther to the north of the previous center and the government of Mexico extended the Tropical Storm Warning northward to Barra El Mezquital.

At 8:00 a.m. EDT on Tuesday the center of Tropical Storm Dolly was located at latitude 23.0°N and longitude 95.7°W which put it about 145 miles east-southeast of La Pesca, Mexico and about 220 miles south-southeast of Brownsville, Texas.  Dolly was moving toward the west-northwest at 13 m.p.h.  The maximum sustained wind speed was 50 m.p.h. and the minimum surface pressure was 1005 mb.  A Tropical Storm Warning is in effect from Tuxpan to Barra El Mezquital, Mexico.

Dolly is expected to continue to move toward the west-northwest and it could make landfall in northern Mexico later today.  The Sea Surface Temperatures in the western Gulf of Mexico are very warm and some further intensification is likely.   Locally heavy rains are possible after Dolly makes landfall.

 

Tropical Depression Five

A low pressure system over the southern Bay of Campeche has been classified as Tropical Depression Five (TD5).  At 5:00 p.m. EDT on Sunday the center of TD5 was located at latitude 20.1°N and longitude 93.6°W which put it about 255 miles east-southeast of Tuxpan, Mexico and about 465 miles south-southeast of Brownsville, Texas.  TD5 was moving toward the west-northwest at 13 m.p.h.  The maximum sustained wind speed was 30 m.p.h. and the minimum surface pressure was 1009 mb.  A Tropical Storm Warning has been issued for the portion of the coast from Tuxpan to La Pesca, Mexico.

TD5 is expected to move toward the west-northwest and intensify into tropical storm Dolly before it makes landfall.  The circulation of TD5 is interacting with a small upper level low north of the system, which is creating some northwesterly shear over it.  The shear is causing most of the thunderstorms and stronger winds to occur southeast of the center.  The shear will also limit intensification over the short term.  Heavy rain may be possible to the north of the center when the system makes landfall.

Possible Bay of Campeche TC

An area of low pressure associated with the northern edge of a tropical wave has moved out over the southern Bay of Campeche.  An Air Force Reserve Hurricane Hunter reconnaissance aircraft is flying through the the system and the plane has found southwesterly winds to 35 m.p.h. on the south side of the disturbance.  The strongest winds are currently on the southern side of the circulation.  If the plane is able to identify a well defined center of circulation at the surface, then the system could be classified as a tropical depression or tropical storm at 5:00 p.m. EDT.

The low pressure system is moving toward the west-northwest at 13 m.p.h.  Many models are predicting that the motion will continue and the system will make landfall in Mexico in the 36-48 hours.  Some intensification is predicted before the system makes landfall.  However, confidence in the model forecasts will increase once a center of circulation is identified and is used to initialize the models.

 

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.