More thunderstorms developed near the center of a slow moving area of low pressure south of Mexico and the National Hurricane Center classified the system as Tropical Storm Vance. At 5:00 p.m. EDT the center of Vance was located at latitude 11.0°N and longitude 101.0°W which put it about 415 miles south of Acapulco, Mexico. Vance was moving toward the west at 5 m.p.h. The maximum sustained wind speed was 40 m.p.h. and the minimum surface pressure was 1005 mb. Vance is the 20th named tropical cyclone for form over the Eastern North Pacific during 2014, which is the most since 1992.
Vance is being steered toward the west by an upper level ridge to its north. Vance is expected to take a long, clockwise path as it moves around the western edge of the ridge. Some recent guidance from numerical models suggests that Vance could move farther westward than was indicated in previous model forecasts. Eventually, when Vance moves farther north, it is anticipated that it will be turned northeastward by a large trough off the west coast of North America. The trough could pull Vance toward the west coast of Mexico sometime next week.
There are southwesterly winds blowing over the top of Vance in the upper levels and the result is that most of the thunderstorms are developing north and east of the center. The shear is expected to decrease on Friday. Vance will be moving over Sea Surface Temperatures (SSTs) that are warmer than 29°C. So, there will be sufficient energy for intensification and some guidance is indicating that Vance could become a hurricane. When the upper level trough begins to affect Vance, the wind shear will increase and it could be on a weakening trend when it turns toward the coast of Mexico next week.
Strong southwesterly winds in the upper troposphere are generating vertical wind shear over the top of Tropical Cyclone Nilofar. The wind shear is blowing the upper part of Nilofar’s circulation northeast of the low level center of circulation and causing the tropical cyclone to weaken rapidly. At 8:00 a.m. EDT on Thursday the center of Tropical Cyclone Nilofar was located at latitude 20.3°N and longitude 64.5°E which put it about 350 miles south-southwest of Karachi, Pakistan and about 550 miles west of Mumbai, India. Nilofar was moving toward the northeast at 7 m.p.h. The maximum sustained wind speed was 50 m.p.h. and there were wind gusts to 65 m.p.h.
An upper level trough to the northwest of Nilofar is pushing strong southwesterly winds over the top of it. There is evidence on satellite imagery that the wind shear may be strong enough to detach the upper portion of Nilofar’s circulation and transport it northeast of the low level center. When the upper portion of the circulation is sheared away and detached, it removes the warm core and eliminates the ability of the cyclone to pump out the mass which is converging on the low level center. If the wind shear were to lessen, Nilofar might be able to re-establish the link between the circulation in the lower and upper levels. However, the wind shear is not expected to diminish and so Nilofar is likely to continue to weaken. It may no longer meet the criteria to be classified as a tropical cyclone in another 24-48 hours.
The lower level circulation of NIlofar is expected to continue toward the northeast in the short term. If the lower level circulation becomes shallow enough, then the southwesterly winds in the upper levels could blow over the top of it. If that happens, then the lower level circulation could drift in the northern Arabian Sea until it spins down. Some of the moisture associated with the circulation of Nilofar could get transported into parts of eastern Pakistan and western India where it could enhance precipitation.
The center of former Tropical Storm Hanna moved steadily toward the west-northwest during the past 18 hours and it recently moved off the coast of Honduras and out over the Gulf of Honduras near Roatan Island. At 3:00 p.m. EDT the center of Tropical Depression Hanna was located at latitude 16.5°N and longitude 87.0°W which put it just west of Roatan Island, about 140 miles east-southeast of Belize City, Belize and about 710 miles south-southwest of Key West, Florida. Hanna was moving toward the west-northwest at 7 m.p.h. The maximum sustained wind speed was 35 m.p.h. and the minimum surface pressure was 1009 mb.
Hanna has a tight, well developed core and thunderstorms are beginning to grow near the center of circulation. The upper level winds over Hanna are light and the Sea Surface Temperatures in the Gulf of Honduras are quite warm. The environment is favorable for intensification, although proximity to land could inhibit strengthening. Hanna probably only has another 12-24 hours to intensify before it makes landfall in Belize, but some intensification is definitely possible.
Clockwise flow around a mid-level ridge of high pressure passing north of Hanna is steering it toward the west-northwest and this general motion is expected to continue. On it’s current track, Hanna will make landfall on the coast of Belize on Wednesday.
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.
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.
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.
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.
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.
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.
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.