Hurricanes Ignacio and Jimena Heading West

Hurricanes Ignacio and Jimena are heading steadily westward over the Pacific Ocean.  At 5:00 p.m. EDT on Friday the center of Hurricane Ignacio was located at latitude 14.6°N and longitude 144.5°W which put it about 785 miles (1260 km) east-southeast of Hilo, Hawaii.  Ignacio was moving toward the northwest at 8 m.p.h. (13 km/h).  The maximum sustained wind speed was 90 m.p.h. (150 km/h) and there were wind gusts to 105 m.p.h. (170 km/h).  The minimum surface pressure was 982 mb.  At 5:00 p.m. EDT on Friday the center of Hurricane Jimena was located at latitude 12.3°N and longitude 123.1°W which put it about 1135 miles (1825 km) southwest of the southern tip of Baja California.  Jimena was moving toward the west at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 105 m.p.h. (170 km/h) and there were wind gusts to 125 m.p.h. (200 km/h).  The minimum surface pressure was 972 mb.

Hurricane Ignacio has remained in a relatively steady state during much of today.  It is moving over water where the Sea Surface Temperature is near 29°C, but an upper level trough near Hawaii is causing some vertical wind shear.  Recent satellite images indicate that an eye may be forming and the core of Ignacio’s circulation is becoming better organized.  Ignacio could strengthen during the next day or so before it moves farther west and the vertical wind shear increases.  A subtropical ridge is steering Ignacio toward the west-northwest and that general motion is expected to continue during the weekend.  Ignacio could be approaching the Big Island of Hawaii in about three days.

Hurricane Jimena intensified rapidly on Friday and it is on the verge of becoming a major hurricane.  It has a very well formed eye with a ring of strong thunderstorms around it.  The upper level winds near Jimena are light and upper level divergence is pumping out mass in all directions.  Jimena is over water where the Sea Surface Temperatures are between 29°C and 30°C and further intensification is likely.  Eye replacement cycles could cause periodic fluctuations in the intensity of Jimena.  Jimena is about 1400 miles (2260 km) east of Ignacio and it could eventually move over some cooler water stirred to the surface by the other hurricane.  The subtropical ridge is also steering JImena toward the west and that motion is expected to continue for the next few days.

Erika Bringing Heavy Rain to the Northeastern Caribbean

Although it is not very well organized, Tropical Storm Erika brought heavy rains to parts of the northeastern Caribbean Sea on Thursday and it caused flooding on Dominica.  At 11:00 p.m. EDT on Thursday the center of Tropical Storm Erika was located at latitude 16.6°N and longitude 65.3°W which put it about 135 miles (215 km) south-southeast of San Juan, Puerto Rico and about 1145 miles (1850 km) east-southeast of Miami, Florida.  Erika was moving toward the west at 17 m.p.h. (28 km/h).  The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1008 mb.  Tropical Storm Warnings have been issued for Puerto Rico, Vieques, Culebra, the U.S. Virgin Islands, the British Virgin Islands, the southeastern Bahamas, the Turks and Caicos, the coast of the Dominican Republic from Isla Saona to the border with Haiti, St. Barthelemy and St. Martin.  Tropical Storm Watches have been issued for the Central Bahamas and the coast of the Dominican Republic from Isla Saona to Punta Palenque.

The circulation around Tropical Storm Erika is poorly organized to due persistent upper level winds from the west which are causing vertical wind shear.  The low level circulation consists of a large diffuse center with at least once smaller mesoscale center rotating around inside the larger diffuse center.  The mesoscale center could have been produced by one of the thunderstorm clusters that form nightly in the southeastern portion of the circulation.  Again on Thursday the strongest thunderstorms occurred east of the center of circulation.  Those thunderstorms produced a lot of upper level divergence but the upper level westerly winds pushed that divergence east of the low level center.  As a result, the surface pressure actually rose a couple of millibars on Thursday.  Stronger thunderstorms are forming southeast of the center of Erika again tonight.  So, the pattern of the past several nights appears to be repeating itself again.

An upper level trough over the western Caribbean Sea is causing the westerly winds that are the source of vertical wind shear over Erika.  That trough is expected to drift west and slowly weaken.  If it does weaken in a couple of days, then the upper level wind pattern could be more favorable for intensification.  However, the center of Erika could pass over or very near Hispaniola.  It is likely that the mountains on that island would significantly disrupt the low level circulation.  If the low level circulation maintains its integrity, the Sea Surface Temperatures around the Bahamas and south Florida are very warm.  If Erika still has a coherent circulation at that time it could organize quickly.

A subtropical ridge is steering Erika toward the west.  Erika is nearing the western end of the ridge and a turn toward the west-northwest is possible.  If Erika gets stronger and the circulation is taller, then the upper level trough could push it more toward the north.  On the other hand, if the circulation of Erika stays weaker and shorter, then lower level flow could push it farther west.  Erika is likely to pass near or over Hispaniola on Friday and on its anticipated track it could be approaching south Florida in about 72 hours.

Even if Erika is a disorganized tropical storm it is capable of producing heavy rains and flooding on any island it crosses.

Tropical Storm Erika Approaches the Leeward Islands

Tropical Storm Erika moved steadily toward the Leeward Islands on Wednesday.  At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Erika was located at latitude 16.7°N and longitude 60.2°W which put it about 110 miles (175 km) east-southeast of Antigua and about 1400 miles east-southeast of Miami, Florida.  Erika was moving toward the west at 16 m.p.h. (26 km/h).  The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1006 mb.  Tropical Storm Warnings have been issued for Anguilla, Saba, St. Eustatius and St. Maarten, Puerto Rico, U.S. Virgin Islands, British Virgin Islands, Montserrat, Antigua, Barbuda, St. Kitts, Nevis, St. Martin and St. Barthelemy.  Tropical Storm Watches have been issued for the coast of the Dominican Republic from Cabo Engano to Cabo Frances Viejo, the southeastern Bahamas and the Turks and Caicos, and Guadeloupe.

Although Erika looks very impressive on infrared satellite images with a large area of cold cloud tops, it is in reality very poorly organized.  The thunderstorms generating those cold clouds are located southeast of the low level center of circulation.  There are not really any thunderstorms in other parts of Erika.  There could be a mid-level center of circulation within the cluster of thunderstorms southeast of the surface center.  Well organized tropical cyclones are vertically stacked with the mid-level center directly above the surface center.  This is certainly not the case with Erika.  Upper level winds from the west appear to be causing vertical wind shear over Erika and that is contributing to the poor organization.

Erika is moving over water where the Sea Surface temperature is almost 29°C.  So, there is sufficient energy in the upper ocean to support intensification.  However, an upper level trough over the central Caribbean Sea could continue to cause wind shear over Erika.  The intensity guidance is inconsistent.  Some guidance strengthens Erika to a hurricane during the next few days, while other guidance weakens it.  Until the circulation become more well organized and thunderstorms develop near the center of circulation, significant intensification is unlikely.  If the vertical wind shear gets any stronger it could weaken Erika to a tropical depression.

The track forecast is also challenging.  The numerical guidance shifted the track toward the east on Wednesday evening, but that was due to the fact that the models were predicting that Erika would become a stronger hurricane.  If it become a stronger storm with a taller, vertically coherent circulation, then the upper trough over the Caribbean could push Erika farther east.  However, if Erika remains weaker, then the winds in the lower levels of the atmosphere could push it farther to the west.  On its anticipated track Erika could approach southeastern Florida in about four days.

 

Ignacio Becomes a Hurricane

The core of Tropical Storm Ignacio organized rapidly on Wednesday and it was upgraded to hurricane status by the National Hurricane Center.  At 11:00 p.m. EDT on Wednesday the center of Hurricane Ignacio was located at latitude 12.2°N and longitude 137.5°W which put it about 1275 miles (2055 km) east-southeast of Hilo, Hawaii.  Ignacio was moving toward the west-northwest at 17 m.p.h. (28 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 992 mb.

A primary rainband wrapped completely around the center of Ignacio and a large eye cleared in the middle of the circulation.   Strong thunderstorms surround the eye in a well formed eyewall.  Other bands of thunderstorms are spiraling around the core of Ignacio.  The upper level winds lessened and the strong convection in the core of Ignacio produced upper level divergence.  The divergence pumped out mass and the surface pressure decreased.  Ignacio is over warm Sea Surface Temperatures.  The environment is favorable for intensification and a period of rapid intensification is possible.  Ignacio could become a major hurricane as it moves across the Central Pacific.

A subtropical ridge is steering Ignacio toward the west.  The ridge is expected to steer the hurricane in a generally west-northwesterly direction during the next few days.  On its anticipated track Ignacio could approach the Big Island of Hawaii in about five days.

Tropical Storm Ignacio Forms Well East of Hawaii

The circulation within a cluster of thunderstorms well to the east of Hawaii became more well organized and the system was classified as Tropical Storm Ignacio.  At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Ignacio was located at latitude 12.3°N and longitude 133.4°W which put it about 1525 miles (2455 km) east-southeast of Hilo, Hawaii.  Ignacio was  moving toward the west at 6 m.p.h. (9 km/h).  The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1003 mb.

The circulation of Tropical Storm Ignacio is still organizing.  Some thunderstorms are located within the core of the tropical storm and more storms are forming in bands around the circulation.  Ignacio is moving over water where the Sea Surface Temperature is near 29°C.  Southeasterly winds in the upper levels are causing some vertical wind shear.  However, some upper level divergence appears to be occurring on the northern side of the circulation.  The environment appears to favor intensification and a period of rapid intensification could occur if an eye starts to form in the core of the tropical storm.

A subtropical ridge is steering Ignacio toward the west and that general motion is expected to continue during the next few days.  On its anticipated track Ignacio would be southeast of Hawaii this weekend.

Tropical Storm Erika Prompts Warnings for the Caribbean

The imminent approach of Tropical Storm Erika prompted the issuance of watches and warnings for locations in the northeastern Caribbean Sea.  At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Erika was located at latitude 16.0°N and longitude 54.4°W which put it about 495 miles (800 km) east of Antigua and about 1780 miles (2870 km) east-southeast of Miami, Florida.  Erika was moving toward the west at 18 m.p.h. (30 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1006 mb.  Tropical Storm Warnings have been issued for Anguilla, Saba, St. Eustatius, and St. Maarten.  Tropical Storm Watches have been issued for Puerto Rico, the U.S. Virgin Islands, the British Virgin Islands, Montserrat, Antigua, Barbuda, St. Kitts, Nevis, Guadeloupe, St. Martin and St. Barthelemy.

For much of Monday the circulation around Tropical Storm Erika consisted of a large swirl of low level clouds and a few thunderstorms well to the southeast of the center.  The minimum surface pressure rose several millibars which was indicative of a weakening storm.  In the past several hours satellite imagery suggests that a few new thunderstorms could be forming closer to the center of circulation.  Erika is moving over water where the Sea Surface Temperature (SST) is between 28°C and 29°C.  So there is plenty of energy in the upper ocean.  The circulation could be pulling in some drier air from farther north of the storm.  There is also some vertical wind shear which may also be inhibiting intensification.    The combination of positive environmental factors like SST and negative environmental factors like drier air and wind shear make the intensity forecast challenging.  Guidance from numerical models is divergent.  Some models predict intensification while others predict that Erika will dissipate like Danny did.  If more thunderstorms continue to develop around the center of circulation, then intensification would be more likely.  On the other hand, if the recently formed thunderstorms dissipate in a few hours, the Erika could weaken to a tropical depression.

A subtropical ridge is steering Erika a little north of due west and that general motion is expected to continue during the next several days.  On its anticipated track Erika would approach the northern Leeward Islands in about 24 hours and it could be near Puerto Rico in less than two days.

Danny Dissipates But Erika Forms Behind It

Vertical wind shear weakened Tropical Storm Danny as it entered the eastern Caribbean Sea and its circulation degenerated into a weak area of low pressure.  However, a new tropical storm formed about a thousand miles east of the remnants of Danny and the National Hurricane Center designated it as Tropical Storm Erika.  At 11:00 p.m. EDT on Monday the center of Tropical Storm Erika was located at latitude 14.4°N and longitude 47.7°W which put it about 955 miles (1535 km) east of the Leeward Islands and about 2240 miles (3600 km) east-southeast of Miami, Florida.  Erika was moving toward the west at 20 m.p.h. (32 km/h).  The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1003 mb.

The circulation around Erika is a little larger than the circulation around Danny was.  There are several bands of thunderstorms near the center of circulation and the thunderstorms are generating upper level divergence in all directions.  Erika is moving over water where the Sea Surface Temperature is near 27.5°C and it will gradually move over warmer SSTs as it moves west.  Erika is moving at 20 m.p.h. and that is about the upper limit for storms that intensify over the tropical Atlantic Ocean.  Currently the low level winds and upper level winds are blowing at nearly the same speed.  So, there is not much vertical wind shear.  However, if Erika were to move toward the west faster, then vertical wind shear could be more significant.  As long as Erika does not move too fast, the environment is favorable for intensification and Danny intensified rapidly over the same region a few days ago.  When Erika enters the Caribbean Sea in two or three days, it could encounter the same upper level trough that sheared Danny apart.

A subtropical ridge is steering Erika quickly toward the west and that same general steering motion is expected to continue for the next two or three days.  Erika could be approaching the northern Leeward Islands in about 48 hours.

Tropical Storm Danny Approaching Dominica and Guadeloupe

Tropical Storm Danny weakened on Sunday but it was maintaining its status as a tropical storm as it approached Dominica and Guadeloupe.  At 11:00 p.m. EDT on Sunday the center of Tropical Storm Danny was located at latitude 15.6°N and longitude 59.8°W which put it about 115 miles (240 km) east-southeast of Guadeloupe and about 1415 miles (2280 km) east-southeast of Miami, Florida.  Danny was moving toward the west at 15 m.p.h. (24 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1009 mb.  Tropical Storm Warnings have been issued for Antigua, Barbuda, Montserrat, St. Kitts and Nevis.  Tropical Storm Watches have been issued for Saba, St. Eustatius and St. Maarten.

Strong southwesterly winds in the upper levels created vertical wind shear which pushed the stronger thunderstorms northeast of the center of circulation.  The core of Tropical Storm Danny consisted of an area of low clouds rotating cyclonically for much of the Sunday, but satellite images and radar indicate that a few more showers and thunderstorms formed during the past few hours.  Danny still has a well defined low level circulation.  Thunderstorms northeast of the center were producing winds to tropical storm force and Danny was still classified as a Tropical Storm at 11:00 p.m. EDT on Sunday.

Upper level southwesterly winds are forecast to continue over the eastern Caribbean Sea.  The resulting vertical wind shear will make it difficult for thunderstorms to persist near the center of Tropical Storm Danny and it could weaken to a tropical depression at any time.  However, it is moving over warm water and a reduction in wind shear could allow for the circulation to maintain itself for a longer period if that happens.

A subtropical ridge north of Danny is steering the tropical storm toward the west and that general motion is expected to continue.  Danny will enter the eastern Caribbean Sea on Monday.  On its anticipated track Danny will pass south of Puerto Rico and it is unlikely to bring much rain to help alleviate the drought conditions there.  Danny could bring some wind and rain to the southern Leeward Islands as it passes over them during the next few hours.

Typhoon Goni Passing West of Okinawa

The center of powerful Typhoon Goni is passing west of Okinawa.  At 11:00 p.m. EDT on Sunday the center of Typhoon Goni was located at latitude 26.9°N and longitude 126.3°E which put it about 125 miles (200 km) west of Okinawa.  Goni was moving northeast at 18 m.p.h. (29 km/h).  The maximum sustained wind speed 125 m.p.h. (200 km/h) and there were wind gusts to 155 m.p.h. (250 km/h).  The minimum surface pressure was 937 mb.

An upper level trough northwest of Goni contributed to the development of an outflow channel which pumped out mass and allowed the typhoon to intensify on Sunday.  Goni is a strong well organized typhoon with an eye and a well formed eyewall.  Spiral bands of thunderstorms are rotating around the core of the circulation.  A weather station on Ishigaki Jima, Japan reported a wind gust to 97 m.p.h. (155 km/h) when Goni passed over the island.  Goni is moving over warm Sea Surface Temperatures (SSTs) and it could maintain its intensity for another 24 hours.  After that time it will move over cooler SSTs and the upper level trough will generate more vertical wind shear.  Goni will finally start to spin down when it moves west of Kyushu.

The upper level trough will continue to pull Goni toward the northeast.  On its anticipated track Typhoon Goni will approach western Kyushu in about 24 hours.  It could bring strong winds and heavy rain to parts of western Japan.

Wind Shear Weakens Danny to a Tropical Storm

Strong upper level winds sheared the top off of Hurricane Danny on Saturday and it weakened to tropical storm intensity.  At 11:00 p.m. EDT on Saturday the center of Tropical Storm Danny was located at latitude 15.6°N and longitude 54.7°W which put it about 480 miles (775 km) east of the Leeward Islands and about 1760 miles (2840 km) east-southeast of Miami, Florida.  Danny was moving toward the west at 15 m.p.h. (24 km/h).  The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 70 m.p.h. (110 km/h).  The minimum surface pressure was 999 mb.  Tropical Storm Watches have been issued for Antigua, Barbuda, Montserrat, St. Kitts, Nevis, Anguilla, Saba, St. Eustatius, St. Maarten, Gudaloupe, St. Barthelemy and St. Martin.

A upper level trough over the eastern Caribbean Sea generated brisk southwesterly winds over the top of Danny and blew the upper portion of the circulation northeast of the low level center.  By late Saturday afternoon the low level center was exposed on satellite imagery.  The vertical wind shear disrupted the vertical circulation of Danny and it weakened fairly quickly.  A few more thunderstorms appear to have developed northeast of the center in recent hours and the wind shear may have decreased just slightly.  Danny will move over slightly warmer water on Sunday, which could add a little more energy to the circulation.  The wind shear is forecast to continue and Danny could weaken further.

As Danny weakened, the lower portion of the circulation was steered more by the winds closer to the surface.  Those winds pushed the center more toward the west.  The subtropical ridge that was steering Danny is expected to strengthen and Danny is forecast to move toward the west for the next day or two.  On its anticipated track Danny could be near the Leeward Islands in about 30 hours and it could be approaching Puerto Rico in 48 hours.