Tag Archives: EP02

Hurricane Aletta Rapidly Intensifies to Category 4

Hurricane Aletta rapidly intensified Friday morning to Category 4 on the Saffir-Simpson Scale.  At 11:00 a.m. EDT on Friday the center of Hurricane Aletta was located at latitude 15.8°N and longitude 111.2°W which put it about 505 miles (815 km) west-southwest of Manzanillo, Mexico.  Aletta was moving toward the west at 5 m.p.h. (8 km/h).  The maximum sustained wind speed was 140 m.p.h. (220 km/h) and there were wind gusts to 165 m.p.h. (265 km/h).  The minimum surface pressure was 943 mb.

An environment with warm Sea Surface Temperatures and little vertical wind shear allowed Hurricane Aletta to intensify rapidly during Thursday night and Friday morning.  A small circular eye was evident at the center of circulation.  A tight ring of strong thunderstorms completely surrounded the eye and the strongest winds were occurring in that ring of storms.  Several bands of strong storms were revolving around the eastern and northern sides of the core of Hurricane Aletta.  Storms around the core were generating very strong upper level divergence which was pumping away large quantities of mass from the hurricane.  The removal of mass allowed the pressure to decrease rapidly and a stronger pressure gradient force generated much stronger winds.

Hurricane Aletta has a relatively small circulation.  Winds to hurricane force extended out about 30 miles (50 km) from the center of circulation.  Winds to tropical storm force extended out about 100 miles (160 km) from the center.  The Hurricane Intensity Index (HII) was 28.3.  The Hurricane Size Index (HSI) was 10.8 and the Hurricane Wind Intensity Size Index (HWISI) was 39.1.  Hurricane Aletta is very similar in intensity and size to Hurricane Charley in 2004 when Charley hit southwest Florida.

Hurricane Aletta will remain in a favorable environment of warm water and little vertical wind shear for another 12 to 24 hours.  So, it could strengthen more in the short term.  Aletta will start to move over cooler water during the next day or so.  There will be less energy in the upper ocean to support the intense hurricane.  In addition, a upper level trough to the northwest of Aletta will produce southwesterly winds which will blow toward the top of the circulation.  Increased vertical wind shear will speed up the rate of weakening.  Since the circulation of Hurricane Aletta is relatively small, it could weaken fairly quickly.

Hurricane Aletta is moving around the southwestern part of a ridge over Mexico.  The ridge has been steering Aletta toward the west.  A turn more toward the northwest is expected when Hurricane Aletta nears the western end of the ridge.  On its anticipated track Hurricane Aletta is forecast to move farther away from the west coast of Mexico.

Aletta Strengthens Into a Hurricane

Former Tropical Storm Aletta strengthened into a hurricane on Thursday.  At 5:00 p.m. EDT on Thursday the center of Hurricane Aletta was located at latitude 15.3°N and longitude 110.0°W which put it about 455 miles (730 km) west-southwest of Manzanillo, Mexico.  Aletta was moving toward the west-northwest at 6 m.p.h. (10 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were wind gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 987 mb.

A circular eye developed at the center of Hurricane Aletta on Thursday afternoon.  The inner ends of several rainbands wrapped part of the way around the eye and a broken ring of thunderstorms surrounded the eye.  The strongest winds were occurring in the broken ring of storms.  Several other bands of showers and thunderstorms were revolving around the core of Hurricane Aletta.  Storm near the core were generating strong upper level divergence which was pumping mass away from the hurricane.  Winds to hurricane force extended out about 25 miles (40 km) from the center of circulation.  Winds to tropical storm force extended out about 90 miles (150 km) from the center.

Hurricane Aletta will move through an environment favorable for intensification during the next 24 to 36 hours.  Aletta will move over water where the Sea Surface Temperature is near 29°C.  It will move through an area where the upper level winds are weak and there will be little vertical wind shear.  Hurricane Aletta is likely to strengthen during the next day or two and it could intensify rapidly if the ring of storms completely encircles the eye.

Hurricane Aletta is moving southwest of a ridge over Mexico which is steering the hurricane toward the west-northwest.  Aletta could move a little more toward the northwest when it reaches the western end of the ridge.  On its anticipated track Hurricane Aletta will move farther away from the west coast of Mexico.

Tropical Storm Aletta Forms West of Mexico

Tropical Storm Aletta formed west of Mexico on Wednesday.  At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Aletta was located at latitude 14.3°N and longitude 108.4°W which put it about 425 miles (680 km) southwest of Manzanillo, Mexico.  Aletta was moving toward the west at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (105 km/h).  The minimum surface pressure was 999 mb.

A distinct low level center of circulation developed within a large area of showers and thunderstorms over the eastern North Pacific Ocean west of Mexico on Wednesday and the National Hurricane Center designated the system as Tropical Storm Aletta.  The circulation of Aletta was still organizing.  Several bands of showers and thunderstorms developed east of the center of circulation.  The bands in the western half of the circulation consisted primarily of showers and low clouds.  Storms near the center of circulation were generating upper level divergence which was pumping mass away from Tropical Storm Aletta.

Tropical Storm Aletta will move through an environment favorable for intensification during the next 48 hours.  Aletta will move over water where the Sea Surface Temperature is near 29°C.  An upper level trough located northwest of Tropical Storm Aletta will produce southwesterly winds which will blow toward the top of the circulation.  Those winds will cause some vertical wind shear, but the shear will not be strong enough to prevent intensification.  Aletta will likely strengthen into a hurricane during the next several days.

Tropical Storm Aletta is moving south of a ridge over Mexico.  The ridge is steering Aletta toward the west.  A general motion toward the west-northwest is forecast for the next several days.  On its anticipated track Tropical Storm Aletta will move farther away from the west coast of Mexico.

Tropical Storm Beatriz Brings Heavy Rain to Southern Mexico

Tropical Depression Two-E intensified into Tropical Storm Beatriz on Thursday and Beatriz brought heavy rain to parts of southern Mexico.  At 5:00 p.m. EDT on Thursday the center of Tropical Storm Beatriz was located at latitude 15.5°N and longitude 96.8°W which put it about 25 miles (40 km) southwest of Puerto Angel, Mexico.  Beatriz was moving toward the north-northeast at 5 m.p.h. (8 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1004 mb.  A Tropical Storm Warning was in effect for the portion of the coast from Salina Cruz to Puerto Escondido.

Tropical Depression Two-E intensified into Tropical Storm Beatriz on Thursday even though its structure evolved into a more asymmetrical system.  Tropical Storm Beatriz appeared to consist of a larger low pressure system which was centered just off the coast of Mexico.  The weather radar from Puerto Angel confirmed that the center of circulation was still offshore.  There were several smaller (mesoscale) counterclockwise rotating circulations that were revolving around the center of the larger low.  At least one of the smaller circulations was already over southern Mexico.  Many of the thunderstorms were occurring in a broad band that wrapped around the eastern and northern portions of the larger low pressure system.  The strongest winds were occurring within this primary rainband.  There were far fewer thunderstorms in the western half of the circulation.  It seemed that after air descended from mountains in Mexico then the air was drawn into the western side of Tropical Storm Beatriz.  The warmer drier air was inhibiting the formation of thunderstorms in the western half of Beatriz.

Although Tropical Storm Beatriz is over water where the Sea Surface Temperature is near 30°C, other environmental factors are unfavorable for intensification.  The proximity to land and the apparent ingestion of drier air are both negative factors.  A narrow upper level ridge oriented from the south-southwest to the north-northeast and a upper level trough to the west of Beatriz are producing brisk southerly winds that are blowing toward the top of the circulation.  Those upper level winds are causing moderate vertical wind shear.  Therefore, Tropical Storm Beatriz is unlike to intensify further during the next several days.

The future track of Tropical Storm Beatriz is uncertain.  If the circulation of Beatriz remains intact then the upper level trough and upper level ridge are likely to steer it toward the north-northeast.  Tropical Storm Beatriz would dissipate over the mountains of Mexico if that scenario occurs.  If the upper level winds are strong enough, the vertical shear could detach the upper portion of the circulation from the low level circulation.  That scenario sometimes occurs when slow moving storms approach the south coast of Mexico.  If that happens, the upper half of the circulation could be transported across Mexico and move over the southern Gulf of Mexico.  Some models are suggesting that a new surface low could form over the southern Gulf in several days, but the wind shear would have to decrease in order for that to occur.  The lower level circulation could be left behind near the coast of Mexico where it would drift slowly near the coast.

Tropical Storm Beatriz is bringing heavy rains to parts of southern Mexico and the heavy rain will continue to fall on Friday.  Locally heavy rain in the more mountainous portions of Oaxaca could create the potential for dangerous flash floods.

Tropical Depression 2E Prompts Tropical Storm Watch By Mexico

The National Hurricane Center designated former Invest 91E as Tropical Depression 2E and the government of Mexico issued a Tropical Storm Watch for the portion of the coast from Salina Cruz to Puerto Escondido.  At 11:00 a.m. EDT on Wednesday the center of Tropical Depression 2E was located at latitude 13.9°N and longitude 97.8°W which put it about 250 miles (400 km) southeast of Acapulco, Mexico.  The depression was moving toward the northeast at 3 m.p.h. (5 km/h).  The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were wind gusts to 40 m.p.h. (65 km/h).  The minimum surface pressure was 1007 mb.

Bands of showers and thunderstorms developed closer to the center of a broad area of low pressure previously designated as Invest 91E on Wednesday morning.  The improved organization prompted the National Hurricane Center to classify the system as Tropical Depression 2E.  Several bands of showers and thunderstorms were revolving around a tighter center of circulation.  Additional bands of showers and thunderstorms were strengthening in the outer portions of the circulation.  Thunderstorms in the inner part of the circulation were beginning to generate upper level divergence which was pumping out mass to the north and west of the depression.

Tropical Depression 2E will be moving through an environment that will be favorable for intensification.  It will be moving over water where the Sea Surface Temperature is 30°C to 31°C.  An upper level ridge centered east of the depression will generate southerly winds which will blow toward the top of the circulation.  Those winds will generate some vertical wind shear, but the shear will not be strong enough to prevent strengthening.  The circulation around the upper level ridge could actually enhance upper level divergence to the north of the depression.  Tropical Depression 2E is likely to intensify into a tropical storm during the next several days.

A subtropical high east of the depression is steering the system slowly toward the northeast.  A slow northerly motion is forecast for the next day or two.  Forecast guidance from the numerical models diverges when the system approaches Mexico.  Some models continue to move the depression inland over Mexico.  Other models suggest that the steering winds will weaken and that the system will stall before it reaches the coast.  The official forecast from the National Hurricane Center has the depression stalling very near the coast and then turning westward during the weekend.

Bands of rain in the outer part of the circulation are already moving over the coast.  Tropical Depression 2E will produce locally heavy rainfall over parts of southern Mexico and there is the potential for dangerous flash floods.

Tropical Depression 2E Intensifies Into Tropical Storm Agatha

Tropical Depression 2E intensified into Tropical Storm Agatha on Saturday morning.  At 11:00 a.m. EDT on Saturday the center of Tropical Storm Agatha was located at latitude 15.6°N and longitude 118.9°W which put it about 775 miles (1245 km) southwest of the southern tip of Baja California.  Agatha was moving toward the west-northwest at 12 m.p.h. (19 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 1005 mb.

The upper level winds blowing over the top to Tropical Depression 2E weakened and the vertical wind shear decreased.  Less vertical wind shear allowed thunderstorms on the northwestern side of the circulation to wrap around the southern side of the center.  With the center of circulation embedded near the main area of thunderstorms the National Hurricane Center named the system Tropical Storm Agatha.  Agatha is a small system and tropical storm force winds only extend out about 45 miles (75 km) from the center.

Agatha has a limited period in which to intensify further.  It is currently moving over water where the Sea Surface Temperature (SST) is near 28°C.  However, Agatha is moving toward cooler SSTs where there will be less energy to drive the circulation.  In addition, there is much drier air north and west of the tropical storm.  Since there is little vertical wind shear, Agatha could intensify during the next 12 to 24 hours.  It will start to weaken when it moves over the cooler SSTs.

A ridge of high pressure north of Agatha is steering the tropical storm toward the east-northwest and that general motion is expected to continue for another day or two.  Agatha currently poses no threat to land.

Agatha was named on July 2.  This is the latest date for the naming of the first tropical storm over the Eastern North Pacific since Ava was named in 1969.

Tropical Depression 2E Forms Southwest of Baja California

After a prolonged period of relatively quiet weather over the Eastern North Pacific Ocean, a tropical depression formed southwest of Baja California.  At 11:00 p.m. EDT on Friday the center of Tropical Depression 2E (TD2E) was located at latitude 14.7°N and longitude 116.7°W which put it about 730 miles (1170 km) southwest of the southern tip of Baja California.  TD2E was moving toward the west-northwest at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were gusts to 40 m.p.h. (65 km/h).  The minimum surface pressure was 1007 mb.

A tropical wave over the Eastern North Pacific Ocean developed a well defined low level circulation and the National Hurricane Center classified the system as Tropical Depression 2E on Friday night.  Although the structure of the low level wind field is symmetrical, most of the thunderstorms are located northwest of the center of circulation.  An upper level ridge north of the depression is generating easterly winds over the top of the circulation.  The vertical wind shear is causing the asymmetrical distribution of the thunderstorms.

The environment around Tropical Depression 2E is marginal for intensification because there are both positive and negative factors.  TD2E is moving over water where the Sea Surface Temperature is near 29°C.  So, there is plenty of energy in the upper ocean to support intensification.  However, the air to the west of the tropical depression is very dry, which will limit the growth of thunderstorms and the formation of rain bands in that part of the system.  In addition moderate vertical wind shear will also inhibit intensification.  Tropical Depression 2E could intensify during the weekend and it has a chance to become the first named storm of the 2016 Eastern Pacific hurricane season.  However, the potential for intensification is limited.

The ridge to the north of TD2E is expected to continue to steer it toward the west-northwest during the next several days.  Tropical Depression 2E poses no threat to land during the next five days.