Author Archives: jay_hobgood

Tropical Cyclone Nilofar Intensifies Into the Equivalent of a Major Hurricane

Light winds in the upper troposphere allowed the circulation around Tropical Cyclone Nilofar to pump out sufficient mass to enable it to intensify into the equivalent of a Major Hurricane.  At 8:00 a.m. EDT on Tuesday the center of Nilofar was located at latitude 16.8°N and longitude 61.8°E which put it about 315 miles southeast of Masirah Island, about 650 miles south-southwest of Karachi, Pakistan and about 740 miles west of Mumbai, India.  Nilofar was moving toward the north at 11 m.p.h.  The maximum sustained wind speed was 135 m.p.h. and there were wind gusts estimated to be 160 m.p.h.

The environment around Nilofar is capable of supporting an intense tropical cyclone, which is what Nilofar has become.  The upper level winds are light, which has allowed upper level divergence to spread the air in all directions.  In addition, the upper level outflow from Nilofar has interacted with surrounding weather systems to create outflow channels to the northeast and to the southwest.  The favorable atmospheric environment combined with warm Sea Surface Temperatures, which are supplying plenty of energy to Nilofar, has produced a strong tropical cyclone.  Nilofar could intensify further, although it is at the intensity where eyewall replacement cycles could begin to cause fluctuations in intensity.

Nilofar is moving around the western end of a subtropical high pressure system which is steering it to the north.  An upper level trough in the westerly flow north of Nilofar will eventually turn it toward the northeast.  Nilofar could threaten parts of Pakistan and India by the end of the week.  However, the southwesterly winds in the upper level trough will also generate more wind shear and Nilofar could start to weaken rapidly when it moves toward the coast of South Asia.

 

Tropical Storm Hanna Forms Near Nicaragua and Honduras

A low pressure system formerly designated as Tropical Depression Nine intensified and it has been classified as Tropical Storm Hanna.  At 11:00 a.m. EDT on Monday the center of Tropical Storm Hanna was located at latitude 14.5°N and longitude 83.2°W which put it about 35 miles north-northeast of Puerto Cabezas, Nicaragua, about 35 miles south of Cabo Gracias a Dios and about 800 miles south-southwest of Key West, Florida.  Hanna was moving toward the west-southwest a 7 m.p.h.  The maximum sustained wind speed was 40 m.p.h. and the minimum surface pressure was 1005 mb.  A Tropical Storm Warning has been issued for the portion of the coast from Puerto Cabezas, Nicaragua to Punta Patuca,, Honduras.

The low pressure system that was once designated Tropical Depression Nine moved southeastward during the weekend.  It eventually moved far enough south to get away from stronger westerly winds to its north and drier air flowing southward over the northwestern Caribbean Sea.  As a result thunderstorms developed near the center of the low and it began to intensify.  Hanna is very close to the coast of Nicaragua and it has a limited time period to intensify before the center moves onshore.

An upper level ridge moving north of Hanna is steering it west-southwestward.  As the upper level ridge moves east, Hanna could turn more toward the west or even west-northwest.  The center of Hanna could move very near the coast of Honduras during the next several days.

The greatest threat from Hanna will be potentially heavy rainfall over Nicaragua and Honduras.

 

The Winds in Tropical Cyclone Nilofar Reach Hurricane Intensity

Tropical Cyclone Nilofar (Tropical Cyclone 04A) intensified on Sunday and it is now the equivalent of a hurricane.  At 8:00 p.m. EDT on Sunday the center of Nilofar was located at latitude 14.8°N and longitude 62.8°E, which put it about 470 miles southeast of Masirah Island, about 750 miles south-southwest of Karachi, Pakistan and about 720 miles west-southwest of Mumbai, India.  Nilofar was moving toward the north-northwest at 5 m.p.h.  The maximum sustained wind speed was 75 m.p.h. and there were wind gusts to 90 m.p.h.

Well developed upper level outflow was pumping out mass and Nilofar intensified steadily on Sunday.  The upper level outflow remains well developed and there appear to be outflow channels to the southwest and northeast.  So, further intensification is possible in the shorter term.  Nilofar is expected to move northward and eventually stronger westerly winds will increase the wind shear and start to weaken the tropical cyclone.

Nilofar has been moving slowly toward the northwest.  It is likely to continue moving northward during the next 24-48 hours.  When Nilofar gets farther north, southwesterly winds on the east side of an upper level trough will turn it more toward the northeast.  Nilofar could eventually make a landfall in Pakistan or India, but the stronger upper level winds will weaken the circulation before it reaches the coast.

 

Tropical Cyclone Forms Over the Arabian Sea

A banded structure developed within an area of thunderstorms over the Arabian Sea and it has been classified as a tropical cyclone.  At 8:00 p.m. EDT on Saturday the center of Tropical Cyclone 04A was located at latitude 14.1°N and longitude 63.0°E which put it about 515 miles south-southeast of Masirah Island.  Tropical Cyclone 04A was moving toward the north at 5 m.p.h.  The maximum sustained wind speed was 40 m.p.h. and there were gusts to 50 m.p.h.

The tropical cyclone had been moving toward the northeast, but it appears to be turning more to northwest in response to a strengthening ridge of high pressure.  It is expected to move toward the northwest during the next 36-48 hours.  As the tropical cyclone approaches Oman, an upper level trough is expected to turn it toward the northeast.  There is some spread in the model guidance about when and where the turn toward the northeast will occur.  Therefore there is greater than normal uncertainty about the track forecast at longer time periods.

Upper level divergence is pumping out mass toward the northeast and southwest of the circulation.  As a result the surface pressure should fall and the tropical cyclone is expected to intensify during the next 48-72 hours.  Winds could reach hurricane force as the tropical moves in the general direction of Oman.

Former Tropical Depression Nine Moves Over Northwestern Caribbean Sea

A small area of low pressure that was classified as Tropical Depression Nine when it was over the Bay of Campeche crossed the Yucatan peninsula and it is now over the northwestern Caribbean Sea.  At 2:00 p.m. EDT on Friday the low was centered at latitude 19.0°N and longitude 87.0°W which put it about 150 miles south of Cancun, Mexico and about 550 miles south-southwest of Key West, Florida.  The low was moving toward the east-northeast at 9 m.p.h.  The maximum sustained wind speed was 25 m.p.h. and the minimum surface pressure was 1008 mb.

Scattered thunderstorms are forming in the vicinity of the low, but the circulation does not appear to be as well organized as it was 24 hours ago.  However, the low is now over water where the Sea Surface Temperatures (SSTs) exceed 29°C Celsius and it appears to be in an area where the winds is diverging in upper levels.  At the same time, there are stronger upper level winds north of the low and drier air from higher latitudes is north and west of the low.  So, some factors in the environment (warm SSTs and upper level divergence) would support intensification, while other factors (nearby wind shear and drier air) would inhibit intensification.  At the  moment most guidance suggest that there is only about a 15% probability that the low will intensify into a tropical cyclone.

However, some guidance from numerical models also suggests that the low could move slowly eastward during the next 24-48 hours as it is affected by an upper level trough passing to its north.  The guidance then suggests that the low could start to move slowly back to the west as an upper level ridge passes north of it.  If the low spends a few days over the warm water of the northwestern Caribbean Sea, then it has the potential to intensify into a tropical cyclone.

 

Tropical Depression Nine Moving Across Yucatan Peninsula

The center of Tropical Depression Nine (TD9) moved inland last night near Ciudad del Carmen, Mexico and TD9 is moving across the Yucatan Peninsula this afternoon.  At 2:00 p.m. EDT on Thursday the center of TD9 was located at latitude 18.1°N and longitude 90.4°W which put it about 190 miles west-northwest of Belize City, Belize and about 750 miles southwest of Key West, Florida.  TD9 was moving toward the east-southeast at 7 m.p.h.  The maximum sustained wind speed was 25 m.p.h. and the minimum surface pressure was 1007 mb.  TD9 is about midway between the Gulf of Mexico and the northwestern Caribbean Sea and it is possible that the center of TD9 could move over the water on Friday.

The low level circulation around TD9 is still well organized and it is possible to see spiral bands rotating counterclockwise around the center on visible satellite imagery.  Some thunderstorms have developed near the center of circulation this afternoon.  Drier air is flowing southward over the Gulf of Mexico and some of that dry air has reached the northern part of the Yucatan peninsula where it is inhibiting the formation of deep convection.  In addition westerly winds in the upper levels are still creating wind shear over the top of TD9.

The higher probability is that the effects of being over land, drier air and wind shear will cause the lower level circulation of TD9 to spin down and dissipate.  The National Hurricane Center is giving this result a probability of 90%.  However, there is a 10% probability that the center of TD9 moves out over the northwestern Caribbean Sea and begins to intensify.  The Sea Surface Temperatures (SSTs) in the northwestern Caribbean Sea are warmer than 29°C and the warm water is fairly deep.  So, there is plenty of energy to support the intensification of a tropical cyclone if TD9 reaches that area.  In addition, as TD9 moves farther south, it will be getting away from the strongest of the upper level winds and the wind shear will start to decrease.  Water vapor will evaporate into the drier air and so it will gradually get moister and have less of an effect on TD9.

If TD9 makes it to the northwestern Caribbean Sea, it could become stationary for several days.  If that happens, then some intensification will be possible.  Of course, before any intensification can occur, it will require that the center of circulation move back over water.  So, the movement of TD9 during the next 24 hours will determine if it dissipates or has a chance to intensify.

 

Tropical Depression Nine Forms Over Bay of Campeche

More thunderstorms formed near the center of a small low pressure system over the Bay of Campeche and the National Hurricane Center classified the low as Tropical Depression Nine (TD9) at 11:00 p.m. EDT on Tuesday.  The center of TD9 was located at latitude 19.4°N and longitude 92.9°W which put it about 160 miles west of Campeche, Mexico and about 850 miles west-southwest of Key West, Florida.  TD9 was moving toward the east at 6 m.p.h.  The maximum sustained wind speed was 35 m.p.h. and the minimum surface pressure was 1000 mb.  The government of Mexico has issued a Tropical Storm Warning for the portion of the coast from Celestun to Frontera.

Westerly winds in the upper levels are still creating wind shear over the top of TD9 and most of the thunderstorms are located in the eastern half of the circulation.  However, the upper level wind speed is expected to diminish and TD9 is likely to intensify into Tropical Storm Hanna on Wednesday.  The westerly winds are also likely to continue to push TD9 toward the east or east-northeast during the next 24 hours.

 

Potential Tropical Cyclone Developing Over Bay of Campeche

A reconnaissance plane found a small center of low pressure within a broader area of low pressure over the Bay of Campeche on Tuesday afternoon.  The plane also found winds to near tropical storm force.  At the 3:00 p.m. EDT the low was centered at latitude 19.3°N and longitude 93.7°W which put it about 350 miles northwest of Campeche, Mexico and about 850 miles west-southwest of Key West, Florida.  The low was moving toward the east at 6 m.p.h.  The maximum sustained wind speed was 38 m.p.h. and the minimum surface pressure of 1001 mb.

Thunderstorms are forming mainly on the southern and eastern sides of the center.  The low could be pulling in some of the drier air over the northern Gulf of Mexico, which may be limiting convection on the northwest side of the low.  Westerly winds in the upper levels are also generating wind shear, which is inhibiting the development of the low.  On the other hand, the low is over Sea Surface Temperatures (SSTs) that are warmer than 29°C and there is plenty of energy in the ocean to support the development of a tropical cyclone.  The pressure has fallen about 5-6 mb in the past 12 hours and so the low appears to be getting stronger.  If more thunderstorms form around the center of the low, it could be classified as a tropical depression or a tropical storm.

The westerly winds in the upper and middle levels are pushing the low slowly toward the east.  Guidance from the forecast models seems to be divided into two main possibilities.  One group of models keeps the low relatively weak and forecasts it to move eastward across the Yucatan peninsula and into the northwestern Caribbean Sea before turning it northeastward and moving the low across the Bahamas.  A second group of models predicts that the low will be a bit stronger and that the upper level flow will turn it northeastward sooner and move the low across southern Florida.  If that second scenario occurs, the low could bring stronger winds and heavy rainfall to parts of south Florida.

 

Possible Tropical Development Over Southern Gulf of Mexico

A low pressure system has formed at the surface along the western end of a stationary front over the Bay of Campeche.  It is possible that this low pressure system could intensify into a tropical cyclone and the National Hurricane Center has tasked a reconnaissance plane to investigate the low tomorrow, if necessary.  At 8:00 a.m. EDT on Monday the low was centered at latitude 19.5°N and longitude 95.5°W which put it about 50 miles east of Veracruz, Mexico and about 940 miles west-southwest of Key West, Florida.  The low as moving toward the northeast at 3 m.p.h.  The maximum sustained wind speed was 30 m.p.h. and the minimum surface pressure was 1008 mb.

The low is over Sea Surface Temperatures (SSTs) that are warmer than 29°C and the southern Gulf of Mexico is a location where we see tropical cyclones develop late in the hurricane season.  On the other hand, westerly winds in the upper levels are creating wind shear over the low pressure system and there is drier air over the northern half of the Gulf of Mexico.  Those two factors will inhibit intensification of the system and so tropical development of the low could be slow.  If thunderstorms do develop near the center of the low, it will remain over warm SSTs while it is in the Gulf of Mexico and it could become a tropical storm.

There is westerly flow in the middle and upper levels over the Gulf of Mexico and that flow is likely to push the low pressure system toward the east.  The low could move slowly during a period while it is organizing.  If an area of deep thunderstorms forms, then the middle and upper level winds could push the low eastward more quickly.  The low could approach southwestern Florida later this week.

 

Hurricane Ana Passing South of Oahu

Although Hurricane Ana is bringing rain to some of the Hawaiian Islands, the core of the storm is passing south of Oahu.  At 11:00 p.m. EDT on Saturday the center of Hurricane Ana was located at latitude 19.9°N and longitude 159.2°W which put it about 130 miles southwest of Honolulu and about 145 miles south of Lihue.  Ana was moving toward the northwest at 8 m.p.h.  The maximum sustained wind speed was 80 m.p.h. and the minimum surface pressure was 987 mb.  A Tropical Storm Warning has been issued for Kauai County including the islands of Kauai and Niihau.  A Tropical Storm Watch remains in effect for Oahu.

A ridge of high pressure that was steering Ana more toward the west is weakening and the hurricane is moving more toward the northwest.  As the steering winds have weakened, the forward speed of Ana has decreased.  Eventually, another ridge of high pressure is expected to build north of Ana and make it turn more toward the west-northwest again.  The Tropical Storm Warning for Kauai was issued as a precaution in case the turn toward the west-northwest is delayed.

An upper level trough northwest of Ana is generating wind shear over the top of the hurricane.  However, the structure has remained relatively intact and a reconnaissance plane found winds to 80 m.p.h. in the northwestern portion of the eyewall.  The intensity of Ana may fluctuate during the next few days as shear increases and decreases.