Monthly Archives: June 2017

Hurricane Dora Weakens South of Baja California

Hurricane Dora weakened as it moved over cooler water south of Baja California on Tuesday.  At 5:00 p.m. EDT on Tuesday the center of Tropical Storm Dora was located at latitude 19.6°N and longitude 111.4°W which put it about 245 miles (400 km) south-southwest of the southern tip of Baja California. Dora as moving toward the west-northwest at 13 m.p.h. (20 km/h).  The maximum sustained wind speed was 65 m.p.h. (105 km/h) and there were wind gusts to 75 m.p.h. (120 km/h).  The minimum surface pressure was 995 mb.

Tropical Storm Dora is moving over water where the Sea Surface Temperature (SST) is near 24°C.  The circulation of Tropical Storm Dora is still very well organized but it is unable to extract sufficient energy from the upper ocean to maintain its intensity.  As a result, the showers and thunderstorms are not rising as far into the atmosphere and the circulation is spinning down.  There is little vertical wind shear and so the circulation is still symmetrical, but it is not as vigorous.  The lack of wind shear will cause the weakening to occur more slowly than it would have if the upper level winds were stronger.

A subtropical ridge is steering Tropical Storm Dora toward the west-northwest and that general motion is expected to continue for anther day or two.  On its anticipated track, Tropical Storm Dora will move farther away from Baja California.  The forecast track would keep Dora over cooler SSTs and it should continue to weaken.

Dora Rapidly Intensifies Into First Eastern Pacific Hurricane of 2017

Tropical Storm Dora intensified rapidly into a hurricane during the overnight hours.  Dora is the first hurricane to develop over the Eastern North Pacific during 2017.  At 11:00 a.m. EDT on Monday the center of Hurricane Dora was located at latitude 17.3°N and longitude 106.3°W which put it about 220 miles (350 km) south of Cabo Corrientes, Mexico.  Dora was moving toward the west-northwest at 13 m.p.h. (20 km/h).  The maximum sustained wind speed was 85 m.p.h. (140 km/h) and there were wind gusts to 100 m.p.h. (160 km/h).  The minimum surface pressure was 985 mb.

The circulation of Hurricane Dora is very well organized.  A circular eye exists at the center of circulation.  A ring of strong thunderstorms surrounds the eye.  Additional bands of showers and thunderstorms are revolving around the core of the circulation.  Thunderstorms in Dora are generating well developed upper level divergence which is pumping large quantities of mass out in all directions.

Dora is a small hurricane.  Wind to hurricane force extend out about 25 miles (40 km) from the center of circulation.  Winds to tropical storm force extend out about 80 miles (130 km) from the center.  The Hurricane Intensity Index (HII) is 12.7.  The Hurricane Size Index (HSI) is 7.3.  The Hurricane Wind Intensity Size Index (HWISI) is 20.0.

Hurricane Dora will move through an environment favorable for intensification for another 12 to 18 hours.  It is currently over water where the Sea Surface Temperature (SST) is near 28°C.  Dora will move over SSTs that will gradually be cooler, but they should be warm enough to support further intensification for another 12 to 18 hours.  Hurricane Dora is moving through an area where upper level winds are weak and there is almost no vertical wind shear.  Hurricane Dora is likely to strengthen further during the next few hours.  Dora will move over much cooler SSTs when it passes south of Baja California and it will begin to weaken on Tuesday.

A subtropical ridge to the north of Dora is steering the hurricane toward the west-northwest and that general motion is expected to continue for another 24 to 48 hours.  On its anticipated track the center of Hurricane Dora will pass south of Baja California.

TD 04E Strengthens Rapidly Into Tropical Storm Dora

Tropical Depression Four-E strengthened rapidly into Tropical Storm Dora on Sunday.  At 11:00 p.m. EDT on Sunday the center of Tropical Storm Dora was located at latitude 16.4°N and longitude 104.3°W which put ti about 290 miles (470 km) south-southeast of Cabo Corrientes, Mexico.  Dora was moving toward the west-northwest at 14 m.p.h. (22 km/h).  The maximum sustained wind speed was 70 m.p.h. (110 km/h) and there were wind gusts to 80 m.p.h. (130 km/h).  The minimum surface pressure was 996 mb.

The circulation of Tropical Storm Dora organized quickly on Sunday.  A primary rainband wrapped tightly around the center of circulation.  An eyelike feature appeared to be forming on microwave and infrared satellite images.  Additional bands of showers and thunderstorms developed outside the core of Tropical Storm Dora.  Thunderstorms around the core generated upper level divergence which pumped out mass in all directions.

Tropical Storm Dora will be moving through an environment very favorable for intensification on Monday.  It will move over water where the Sea Surface Temperature (SST) is near 29°C.  An upper level ridge over Mexico is producing easterly winds that are blowing toward the top of the circulation, but there is little vertical wind shear.  A combination of warm water and little shear will allow Dora to intensify into a hurricane during the next 24 hours.  The rate of intensification could increase once the formation of the eye is complete.  Dora will move over cooler SSTs on Tuesday.  The cooler SSTs will initially halt the intensification.  When Dora is unable to extract sufficient energy from the upper ocean it will start to weaken.

A subtropical ridge northeast of Dora is steering the tropical storm toward the west-northwest and a general west-northwesterly motion is expected to continue for another day or two.  On its anticipated track the center of Tropical Storm Dora will remain southwest of Mexico.  Dora will pass south of Baja California on Tuesday.

Tropical Depression Four-E Forms South of Acapulco

Tropical Depression Four-E formed south of Acapulco, Mexico on Saturday.  At 11:00 p.m. EDT on Saturday the center of Tropical Depression Four-E was located at latitude 14.3°N and longitude 100.0°W which put it about 180 miles (290 km) south of Acapulco.  It was moving toward the west-northwest at 10 m.p.h. (16 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 1006 mb.

A distinct surface center of circulation developed within a larger area of thunderstorms south of Mexico on Saturday.  Showers and thunderstorms began to consolidate near the center.  Additional bands of showers and thunderstorms formed outside the core of the circulation.  The thunderstorms began to produce upper level divergence which pumped mass away from the core of the depression.

Tropical Depression Four-E will move through an environment favorable for intensification during the next several days.  It will move over water where the Sea Surface Temperature is near 30°C.  An upper low over the western Gulf of Mexico is enhancing the upper level divergence to the northeast of the tropical depression.  An upper level ridge over Mexico is producing easterly winds which are blowing toward the top of the circulation, but the vertical wind shear is minimal.  Tropical Depression Four-E could intensify in a tropical storm on Sunday.  It has a chance to become a hurricane early next week before it reaches cooler water south of Baja California.

A subtropical ridge over Mexico is steering Tropical Depression Four-E toward the west-northwest and that general motion is expected to continue for another two or three days.  On its anticipated track the center of Tropical Depression Four-E is expected to remain south of the coast of Mexico.  Rainbands in the northern portion of the circulation could produce locally heavy rain over parts of southern Mexico.  The greatest risk would be for flash floods in those areas.

Tropical Depression Cindy Brings Stormy Weather to Southern U.S.

Tropical Depression Cindy brought stormy weather to parts of the southern U.S. on Thursday.  At 11:00 p.m. EDT on Thursday the center of Tropical Depression Cindy was located at latitude 33.1°N and 93.5°W which put it about 70 miles (115 km) southwest of Little Rock, Arkansas.  Cindy was moving toward the north-northeast at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 20 m.p.h. (30 km/h) and there were wind gusts to 30 m.p.h. (50 km/h).  The minimum surface pressure was 1000 mb.

Tropical Storm Cindy made landfall early on Thursday morning near the border between Texas and Louisiana.  Cindy moved steadily northward during the day and it was centered over southwestern Arkansas by Thursday night.  Broad counterclockwise rotation around Cindy transported warm and very humid air over the southern U.S.  Bands of showers and thunderstorms dropped locally heavy rain in some places.  Rivers and streams were above flood stage in several southern states.  Flash Flood Warnings and Flash Flood Watches were issued for portions of the southern U.S. and Ohio River Valley.  Several tornadoes formed in the bands of thunderstorms.  A tornado in Alabama caused property damage.  Southerly winds blowing toward the shore were still causing storm surges along the northern coast of the Gulf of Mexico.

Tropical Depression Cindy is forecast to move northeast toward the Ohio River Valley on Friday.  It will continue to produce locally heavy rain.  A slow moving cold front will approach the region from the west.  A band of stronger convergence could develop where the counterclockwise flow around Cindy interacts with the flow along the cold front.  Higher rainfall totals may occur where this interaction happens.  Wind shear created by the interacting weather systems could also create the potential for some tornadoes.  Tropical Depression Cindy could merge with the cold front during Friday night or Saturday.

Tropical Storm Cindy Nears Northwest Gulf Coast

Tropical Storm Cindy neared the northwestern coast of the Gulf of Mexico on Wednesday evening.  At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Cindy was located at latitude 28.6°N and longitude 93.4°W which put it about 95 miles (150 km) south-southeast of Port Arthur, Texas.  Cindy was moving toward the north-northwest 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 60 m.p.h. (95 km/h).  The minimum surface pressure was 992 mb.

A Tropical Storm Warning is in effect for the portion of the coast from San Luis Pass, Texas to Grand Isle, Louisiana.

Tropical Cyclone Cindy exhibits a hybrid structure in which a broad surface low pressure system is interacting with an upper low centered near the Upper Texas coast.  There is a distinct center of low pressure at the surface.  A band of showers and thunderstorms is northwest of the surface center.  Drier air in the middle and upper levels wraps around the southern and eastern sides of the center and there are no thunderstorms in those quadrants of the core of Tropical Storm Cindy.  A broad flow of moisture is producing bands of showers and thunderstorms in the outer portions of the eastern and northern sides of the circulation.

Tropical Storm Cindy is moving around the western end of a subtropical high pressure system centered over the Atlantic Ocean.  The subtropical high is steering Cindy toward the north-northwest.  On its anticipated track Tropical Storm Cindy will make landfall near the border between Texas and Louisiana on Thursday.  Cindy will turn toward the north and then the tropical storm will move northeastward on Friday.

Some locations will experience prolonged periods of rainfall and fresh water flooding will be possible in those area.  There could also be a storm surge of 3 to 6 feet (1 to 3 meters) near where the center makes landfall.  A few tornadoes could be spun up as rainbands move over the coast.

Tropical Storm Cindy Strengthens Over the Central Gulf of Mexico

Tropical Storm Cindy strengthened on Tuesday night as is moved slowly over the Central Gulf of Mexico.  At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Cindy was located at latitude 26.4°N and longitude 91.0°W which put it about 305 miles (495 km) southeast of Galveston, Texas.  Cindy was moving toward the northwest at 7 m.p.h. (11 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 997 mb.

A Tropical Storm Warning is in effect for the portion of the coast from San Luis Pass, Texas to the Alabama/Florida border including Metropolitan New Orleans and Lake Pontchartrain.

Although Tropical Storm Cindy does not look very impressive on infrared satellite imagery, data from reconnaissance aircraft and surface observations from buoys and ships indicate that it has strengthened during the past few hours.  Tropical Storm Cindy displays the structure of a highly sheared tropical storm.  There are no thunderstorms near the center of circulation.  Most of the showers and thunderstorms are in bands well to the east and north of the center of circulation.  The circulation of Tropical Storm Cindy is large and winds to tropical storm force extend out about 275 miles (445 km) northeast of the center.

A combination of an upper level low to the northwest of Cindy and an upper level ridge to the east of it have generated enough upper level divergence to cause the surface pressure to decrease.  The lower pressure at the center created a bigger pressure difference with the subtropical high over the Atlantic Ocean and the stronger pressure gradient force accelerated the wind speed.  So, even though the upper level low produced enough vertical wind shear to prevent a classical process of tropical intensification in Tropical Storm Cindy, the larger scale weather features combined to produce a stronger, larger tropical storm.

Tropical Storm Cindy could intensify a little more if the large scale environment pumps out more mass and the surface pressure decreases further.  The tropical storm could also intensify if the upper low moves farther away from Cindy and the wind shear decreases.  It is unlikely that Tropical Storm Cindy will intensify into a hurricane, but there is a slight possibility that could occur before it makes landfall.

The subtropical high over the Atlantic Ocean is steering Tropical Storm Cindy slowly toward the northwest and that general motion is expected to continue for another 12 to 24 hours.  Cindy could gradually turn toward the north as it approaches the coast and the tropical storm will turn toward the northeast after it moves inland.  On its anticipated track the center of Tropical Storm Cindy could approach the northwestern coast of the Gulf of Mexico on Wednesday night.

The large size of the circulation of Tropical Storm Cindy and its slow motion mean that locally heavy rain and flooding are the greater risks.  There is also the potential for rainbands to spin up tornadoes when they move onto the coast.  Southerly winds driving water toward the coast are already causing a storm surge along parts of the coast of Louisiana.  A storm surge of 3 to 6 feet (1 to 2 meters) may be possible where the strongest winds strike the coast.

Potential Tropical Cyclone Three Prompts Warnings and Watches for Louisiana and Texas

An area of low pressure designated Potential Tropical Cyclone Three moved into the Gulf of Mexico on Monday and the National Hurricane Center issued Tropical Storm Warnings and Watches for Louisiana and Texas.  At 11:00 p.m. EDT on Monday the center of Potential Tropical Cyclone Three was located at latitude 24.4°N and longitude 89.5°W which put it about 380 miles (610 km) south-southeast of Morgan City, Louisiana.  It was moving toward the north-northwest at 8 m.p.h. (13 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 1000 mb

A Tropical Storm Warning is in effect for the portion of the coast from Intracoastal City, Louisiana to the mouth of the Pearl River.  A Tropical Storm Watch has been issued for the portion of the coast from High Island, Texas to Intracoastal City, Louisiana.

The circulation of Potential Tropical Cyclone 03 is not very well organized.  The system does have a well defined low level center of circulation.  However, there are no thunderstorms near the low level center.  All of the strong showers and thunderstorms are occurring in bands well to the east of the center of circulation.  Some of those bands do contain winds to tropical storm force.  An upper level low over the northwestern Gulf of Mexico is producing strong southwesterly winds which are blowing over the top of the low level center.  The strong vertical wind shear created by those winds is preventing the development of storms closer to the low level center.

The environment around Potential Tropical Cyclone 03 will remain unfavorable for intensification on Tuesday.  The system will move move water where the Sea Surface Temperature is near 29°C.  So, there will be enough energy to support intensification.  However, the upper level low will continue to produce strong vertical wind shear over the low level center of circulation.  The upper low is forecast to move slowly toward the northwest.  It is possible that the strength of the upper level winds over the northwestern Gulf of Mexico could diminish in a day or two.  If the shear decreases, thunderstorms could form closer to the center and if the structure of the system takes on a more tropical appearance, it could be designated Tropical Storm Cindy.

Potential Tropical Cyclone 03 is moving around the western end of the subtropical high over the Atlantic Ocean.  The high is steering the system toward the north-northwest and that general motion is expected to continue.  On its anticipated track Potential Tropical Cyclone 03 is expected to approach the coast of Louisiana in about 48 hours.  The steering winds could weaken when the system gets closer to the coast and the uncertainty about the future track increases after about 48 hours.

Strong southerly flow on the eastern side of Potential Tropical Cyclone 03 will bring very humid air over the southeastern U.S.  The biggest risk is likely to be heavy rain and the potential for floods.  The system will also bring gusty winds and some storm surge to parts of the coast.

Tropical Storm Bret Forms Near Trinidad

An Air Force Reserve Hurricane Hunter aircraft investigated Potential Tropical Cyclone 02 on Monday afternoon as it moved closer to Trinidad and the plane found a closed circulation.  Based on data from the reconnaissance plane the National Hurricane Center classified the system as Tropical Storm Bret.  At 8:00 p.m. EDT on Monday the center of Tropical Storm Bret was located at latitude 9.5°N and longitude 60.5°W which put it about 85 miles (135 km) southeast of Trinidad.  Bret was moving toward the west-northwest at 25 m.p.h. (40 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 1008 mb.

Tropical Storm Warnings are in effect for Grenada, Trinidad, Tobago and the coast of Venezuela from Pedernales to Cumana.  Tropical Storm Watches have been issued for Aruba, Bonaire, and Curacao.

The reconnaissance plane found a well organized center of circulation at the surface.  The strongest winds were occurring in vigorous bands of thunderstorms located north of the center of circulation.  Weaker showers and thunderstorms were occurring in bands south of the center of circulation.  The thunderstorms north of the center were generating upper level divergence which was pumping mass away to the north of the tropical storm.  The circulation of Tropical Storm Bret is fairly small.  Winds to tropical storm force only extend out about 80 miles (130 km) to the north of the center of circulation.

Tropical Storm Bret will move through an environment that will only be marginally favorable for intensification on Tuesday.  Bret will move over water where the Sea Surface Temperature is near 29°C.  An upper level ridge east of Bret and an upper level trough to the west are producing southerly winds which are generating moderate vertical wind shear.  The vertical wind shear may be responsible for the asymmetrical distribution of thunderstorms.  The shear will also inhibit intensification during the next 24 hours, although some intensification may possible.  When Bret moves into the Caribbean Sea, the vertical wind shear will increase.  Tropical Storm Bret will also move very close to the north coast of Venezuela.  It could pull drier air from South America into the southern part of the circulation, which would contribute to further weakening.

The subtropical high pressure system over the Atlantic Ocean is steering Tropical Storm Bret rapidly toward the west-northwest.  A fast west-northwesterly motion is forecast to continue for several more days.  On its anticipated track Tropical Storm Bret will move across Trinidad, near the north coast of Venezuela and toward Aruba, Bonaire, and Curacao.  It will bring gusty winds and locally heavy rain to all of those places.

Invest 92L Becomes Potential Tropical Cyclone Two, Warnings Issued for Windward Islands

The National Hurricane Center (NHC) changed the designation of Invest 92L to Potential Tropical Cyclone 02 on Sunday evening.  NHC implemented a new policy for 2017 which allows it to issue tropical cyclone watches and warnings before it officially classifies a system as a tropical cyclone.  NHC issued Tropical Storm Warnings for some of the Windward Islands because of Potential Tropical Cyclone 02 on Sunday evening in accordance with the new policy.

At 11:00 p.m. EDT on Sunday the center of Potential Tropical Cyclone 02 was located at latitude 7.9°N and longitude 52.4°W which put it about 630 miles (1015 km) east-southeast of Trinidad.  It was moving toward the west-northwest at 23 m.p.h. (37 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.

Tropical Cyclone Warnings have been issued for Barbados, St. Vincent, the Grenadines, Grenada, Trinidad, and Tobago.

The circulation of Potential Tropical Cyclone 02 appeared to get better organized on Sunday evening.  Satellite imagery seemed to indicate that a more circular area of thunderstorms was forming around the center of circulation.  The system was already producing sustained winds to 40 m.p.h. (60 km/h) and if a center of circulation develops, it will be classified as a tropical storm.

Potential Tropical Cyclone 02 will move through an environment that will be somewhat favorable for intensification during the next 24 hours.  It will move over water where the Sea Surface Temperature is near 29°C.  An upper level trough over the eastern Caribbean Sea is generating southwesterly winds that are causing some vertical wind shear.  Potential Tropical Cyclone 02 has about 24 to 36 hours before the shear increases significantly.  After that time the system will weaken.

A subtropical high pressure system over the Atlantic is steering Potential Tropical Cyclone 02 toward the west-northwest.  A general west-northwesterly motion is expected to continue.  On its anticipated track Potential Tropical Cyclone 02 will reach the southern Windward Islands later on Monday.  It will bring gusty winds and locally heavy rain when it gets there.