Monthly Archives: August 2017

Hurricane Irma Strengthens Rapidly Over Atlantic

Hurricane Irma strengthened rapidly as it moved over the tropical Atlantic Ocean.  At 11:00 a.m. EDT on Thursday the center of Hurricane Irma was located at latitude 16.9°N and longitude 33.8°W which put it about 1845 miles (2975 km) east of the Leeward Islands.  Irma was moving toward the west-northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 100 m.p.h. (160 km/h) and there were wind gusts to 120 m.p.h. (195 km/h).  The minimum surface pressure was 979 mb.

Hurricane Irma intensified rapidly on Thursday morning.  A circular eye developed at the center of circulation and a ring of strong thunderstorms surrounded the eye.  Numerous bands of showers and thunderstorms developed outside the core of Irma.  Hurricane Irma has a very circular, symmetrical shape.  Thunderstorms in the core of Irma were generating strong upper level divergence which was pumping mass away in all directions from the hurricane.

Hurricane Irma will move through an environment favorable for intensification during the next few days.  Irma will move over water where the Sea Surface Temperature is near 28°C.  Irma is under the western end of an upper level ridge, but the upper level winds are weak and there is not much vertical wind shear.  Irma is likely to intensify during the next few days and it is forecast to become a major hurricane.  Hurricanes that intensify rapidly often develop concentric eyewalls, which cause fluctuations in their intensity.  It is highly likely that Hurricane Irma will go through one of more eyewall replacement cycles which will cause temporary fluctuations in the wind speed.  Eyewall replacement cycles often result in a larger hurricane and Hurricane Irma has the potential to develop into a big classic Cape Verde hurricane.

Hurricane Irma is nearing a weaker region in the subtropical ridge to its north.  The weakness is allowing Irma to move toward the west-northwest.  The ridge is expected to strengthen and steer Hurricane Irma more toward the west or west-southwest during the next few days.  On its anticipated track Hurricane Irma is forecast to be a major hurricane east of the Leeward Islands in five days.  The uncertainty about the future track of Hurricane Irma increases after that time.  People around the western Atlantic need to monitor the progress of Hurricane Irma.

Typhoon Sanvu Brings Wind and Rain to Chichi Jima

Typhoon Sanvu is bringing a prolonged period of gusty winds and heavy rain to Chichi JIma, Japan.  Sanvu strengthened during the past several days while it meandered around Chichi Jima.  At 11:00 a.m. EDT on Thursday the center to Typhoon Sanvu was located at latitude 28.1°N and longitude 142.0°E which put it about 60 miles (95 km) north-northwest of Chichi Jima, Japan.  Sanvu was moving toward the north at 8 m.p.h. (13 km/h).  The maximum sustained wind speed was 85 m.p.h. (135 km/h) and there were wind gusts to 105 m.p.h. (170 km/h).  The minimum surface pressure was 967 mb.

The organization of Typhoon Sanvu has been slowly improving.  An eye developed at the center of Sanvu as the typhoon moved slowly over Chichi Jima.  A broken ring of thunderstorms surrounds the eye.  The strongest winds are occurring in the ring of storms.  A primary band of thunderstorms wraps around the western and southern sides of the center of circulation.  Other bands of showers and thunderstorms are developing outside the core of Typhoon Sanvu.  Most of the bands are developing in the southern half of the circulation.  Thunderstorms in the core of Sanvu are producing upper level divergence which is pumping mass away to the north of the typhoon.

Typhoon Sanvu will move through an environment favorable for intensification for several more days.  It will move over water where the Sea Surface Temperature is near 30°C.  An upper level ridge east of Sanvu is producing southerly winds which are blowing toward the top of the circulation, but there is not much vertical wind shear.  Typhoon Sanvu is likely to continue to strengthen for another 24 to 48 hours.  Eventually, Sanvu will move over colder water and the wind shear will increase.  It will start to weaken when that happens.

Sanvu is moving around the western end of a subtropical ridge which steering the typhoon toward the north.  When Typhoon Sanvu moves farther north, it will be steered by an upper level trough over Japan.  Southwesterly winds will steer Sanvu toward the northeast at a faster speed in a day or two.  On its anticipated track Typhoon Sanvu would stay east of Tokyo, but it could affect the northernmost islands of Japan in four or five days.  Conditions in Chichi Jima should improve slowly as Typhoon Sanvu moves farther away.

Tropical Storm Harvey Moves Into Louisiana, Irma Strengthens Quickly

Tropical Storm Harvey finally moved into Louisiana on Wednesday after lingering for several days over the northwestern Gulf of Mexico.  Harvey weakened to a tropical depression after it moved inland.  At the same time a new tropical storm named Irma strengthened quickly over the eastern Atlantic Ocean.  At 11:00 p.m. EDT on Wednesday the center of Tropical Depression Harvey was located at latitude 31.7°N and longitude 92.3°W which put it about 30 miles (50 km) north-northeast of Alexandria, Louisiana.  Harvey was moving toward the north-northeast at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 998 mb.

After dropping record rainfall and causing destructive floods of parts of southeastern Texas and western Louisiana, Tropical Depression Harvey finally started to move steadily toward the north-northeast on Wednesday.  Harvey was still producing heavy rain over parts of western Louisiana, but the fact that it was moving should limit the total rainfall at any location.  Bands of showers and thunderstorms on the far eastern periphery of Harvey’s circulation were also dropping heavy rain.  Some of those thunderstorms were strong enough to approach severe criteria.  Tropical Depression Harvey is forecast to move toward the Ohio River Valley during the next several days and it will bring windy, wet weather to the Middle Mississippi and Ohio River Valleys.  Rain associated with the circulation of Tropical Depression Harvey could also reach the Mid-Atlantic States later this week.

At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Irma was located at latitude 16.4°N and longitude 32.2°W which put it about 545 miles (875 km) west of the Cabo Verde Islands.  Irma was moving toward the west at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 65 m.p.h. (105 km/h) and there were wind gusts to 80 m.p.h. (130 km/h).  The minimum surface pressure was 999 mb.

The circulation of Tropical Storm Irma organized quickly on Wednesday.  Numerous bands of showers and thunderstorms formed and began to revolve around a well organized center of circulation.  Thunderstorms in the core of Irma generated well developed upper level divergence which pumped away mass in all direction.  There were occasional satellite images which hinted that an eye could be forming at the center of Tropical Storm Irma.

Tropical Storm Irma will be moving through an environment that will be favorable for intensification.  Irma will move over water where the Sea Surface Temperature is near 28°C.  The upper level winds are weak and there is little vertical wind shear.  Irma is likely to become a hurricane on Thursday and it could intensify rapidly if an eye forms.  Tropical Storm Irma is forecast to become a major hurricane and it could become one of the big classic Cape Verde hurricanes.

A strong subtropical high to the north of Irma is steering the tropical storm toward the west and a general westerly motion is forecast to continue for the next few days.  There is more divergence in the model guidance after a few days and the future track of Irma when it nears the Lesser Antilles is more uncertain.  Tropical Storm Irma has the potential to become a big dangerous hurricane and it will need to be watched carefully.

Tropical Storm Lidia Threatens Baja California

Tropical Storm Lidia became an increased threat to Baja California as it moved closer on Wednesday night.  At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Lidia was located at latitude 20.7°N and longitude 109.2°W which put it about 160 miles (255 km) south-southeast of the southern tip of Baja California.  Lidia was moving toward the north-northwest at 7 m.p.h. (11 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 1001 mb.

A Hurricane Watch is in effect for the portion of the coast from Puerto Cortes to La Paz, Mexico including Cabo San Lucas.  A Tropical Storm Warning is in effect for the portion of the coast from Puerto Cortes to San Evaristo including Cabo San Lucas and from Tempehuaya to Huatabampito, Mexico.  A Tropical Storm Watch is in effect for the portion of the coast from San Evaristo to Loreto, Mexico and from Puerto Cortes to Puerto Andresito.

A distinct center of circulation began consolidating in a large area of low pressure previously designated Potential Tropical Cyclone Fourteen-E on Wednesday.  Numerous bands of showers and thunderstorms started developing around the consolidating center.  There were more showers and thunderstorms in the southern half of the circulation than there were in the northern half of the circulation.  Thunderstorms southwest of the center of circulation were beginning to generate some upper level divergence, but it was not well developed.  Tropical Storm Lidia formed out of a large low pressure system and it still has a large circulation.  Winds to tropical storm force extend out about 120 miles (195 km) from the center on the eastern side of Lidia.

Tropical Storm Lidia was in an environment that was marginally favorable for intensification on Wednesday.  Lidia was moving over water where the Sea Surface Temperature was near 30°C.  An upper level ridge to the east of Lidia was producing westerly winds which were causing moderate vertical wind shear, especially over the northern half of the circulation.  The environment around Tropical Storm Lidia is forecast to become a little more favorable for intensification on Thursday.  The upper level winds are forecast to become weaker, which would reduce the wind shear.  Lidia will still be moving over very warm water and it should intensify on Thursday.  The rate of intensification could increase as the core of the tropical storm becomes more organized.  There is a chance that Lidia could strengthen into a hurricane which is why there is a Hurricane Watch for part of Baja California.

Lidia is moving around the western end of a subtropical ridge, which is steering the tropical storm toward the north-northwest.  A general north-northwesterly motion is expected to continue for another day or two.  On its anticipated track the center of Tropical Storm Lidia could reach the southern tip of Baja California by Thursday evening.  In addition to gusty winds Tropical Storm Lidia will produce very heavy rain.  Heavy rain falling on the steep terrain of Baja California creates the risk of flash floods.

Potential Tropical Cyclone Fourteen-E Prompts Hurricane Watch for Baja California

The National Hurricane Center is forecasting that a weather system currently designated as Potential Tropical Cyclone Fourteen-E will become a tropical storm and affect Baja California.  The government of Mexico has issued a Hurricane Watch and a Tropical Storm Warning for the portion of the coast from Todos Santo to Los Barriles including Cabo San Lucas.

At 5:00 p.m. EDT on Tuesday the center of Potential Tropical Cyclone Fourteen-E was located at latitude 17.2°N and longitude 107.2°W which put it about 430 miles (695 km) south-southeast of the southern tip of Baja California.  It was moving toward the 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 wind gusts to 40 m.p.h. (65 km/h).  The minimum surface pressure was 1006 mb.

The circulation of Potential Tropical Cyclone Fourteen-E is in the early stages of organization.  There is a large counterclockwise circulation over the Eastern North Pacific Ocean west of Mexico.  Numerous showers and thunderstorms are forming within the circulation, but there is no well defined center of circulation.  There are fewer showers and thunderstorms in the eastern portion of the circulation.  An upper level ridge centered over Mexico is generating brisk easterly winds which are blowing over the top of the circulation.  Those winds are causing moderate vertical wind shear and the system has not yet begun to generate much upper level divergence.

Potential Tropical Cyclone Fourteen-E will move through an environment that will be somewhat favorable for intensification.  It will move over water where the Sea Surface Temperature is near 30°C.  So, there is plenty of energy in the upper ocean to support intensification.  The strength of the upper level winds is forecast to diminish and the wind shear is likely to decrease.  If the wind shear decreases, then the environment will become more favorable for intensification.  Intensification is likely to be slow while the circulation becomes more organized and develops a distinct low level center.  Potential Tropical Cyclone Fourteen-E could become a tropical storm on Wednesday.  It has a chance to intensify to a hurricane on Thursday.

Potential Tropical Cyclone Fourteen-E is moving around the western end of a subtropical ridge.  The ridge is steering the system toward the northwest and a general northwesterly motion is expected to continue for another day or two.  On its anticipated track the center of Potential Tropical Cyclone Fourteen-E could approach the southern part of Baja California by late on Thursday.  It could be a strong tropical storm or a hurricane at that time.  Locally heavy rain falling on the steep terrain of Baja California always creates a risk for flash floods.

Tropical Storm Harvey’s Record Rains Continue Over Texas and Louisiana

The record setting rainfall from Tropical Storm Harvey continued over southeastern Texas and Louisiana on Tuesday morning.  A rain gauge southeast of Houston near Mary’s Creek at Winding Road has measured 49.20 inches (125 cm) of rain from Tropical Storm Harvey as of 9:00 a.m. CDT on Tuesday.  This total sets a new record for the most rainfall from a tropical cyclone over the contiguous 48 states of the U.S.  The previous record was 48 inches (122 cm) dropped by Tropical Cyclone Amelia in 1978 over Medina, Texas.

At 11:00 a.m. EDT on Tuesday the center of Tropical Storm Harvey was located at latitude 28.4°N and longitude 94.3°W which put it about 115 miles (185 km) south-southwest of Cameron, Louisiana.  Harvey 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 997 mb.

A Tropical Storm Warning is in effect for the portion of the coast from Port O’Connor, Texas to Morgan City, Louisiana.  A Tropical Storm Watch is in effect for the portion of the coast from Morgan City to Grand Isle, Louisiana.

The center of Tropical Storm Harvey moved back over the Gulf of Mexico late on Monday and it is currently over the northwestern Gulf.  Harvey is still producing heavy rain over southeastern Texas and parts of Louisiana.  There is still a well defined center and strong counterclockwise rotation in the lower levels of the atmosphere.  Dry air wrapped around the circulation of Harvey and there are mainly lighter showers near the center of the tropical storm.  There are several stronger bands of thunderstorms on the eastern periphery of the circulation.  Those bands are dropping heavier rain over eastern Louisiana and parts of Mississippi.  The strong counterclockwise rotation is transporting moist air over land.  Increased friction over the land is causing more convergence which is pushing the air upwards.  Stronger rising motion is generating areas of heavier rain over southeast Texas and southern Louisiana.  In addition, the land is warming during the day, which is making the lower atmosphere more unstable and contributing to the heaver rain.

Flood Watches and Warnings are in effect from Northwest Florida to Southeast Texas because of the potential for more heavy rain.  Tropical Storm Harvey is finally starting to move slowly toward the north-northeast.  It should make a landfall on the coast of Louisiana early on Wednesday.  Tropical Storm Harvey will weaken as it moves farther inland and it should move over the Lower Mississippi River Valley as a tropical depression late this week.  The rain over southeastern Texas and southern Louisiana should end once Harvey moves farther inland.

Elsewhere, a low pressure system designated Potential Tropical Cyclone Ten was bringing gusty winds and higher waves to portions of the Mid-Atlantic coast.  At 11:00 a.m. EDT on Tuesday the center of Potential Tropical Cyclone Ten was located at latitude 34.4°N and longitude 77.2°W which put it about 35 miles (60 km) west-southwest of Cape Lookout, North Carolina.  It was moving toward the northeast at 17 m.p.h. (28 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1006 mb.  A Tropical Storm Warning was in effect from Cape Lookout to Duck, North Carolina including Pamlico and Albemarle Sounds.  Potential Tropical Cyclone Ten is forecast to merge with a front and become a strong extratropical cyclone over the western Atlantic Ocean.

Tropical Storm Sanvu Forms Over Northern Marianas

Tropical Storm Sanvu formed over the northern Marianas on Monday.  At 11:00 a.m. EDT on Monday the center of Tropical Storm Sanvu was located at latitude 20.4°N and longitude 146.4°E which put it about 100 miles (160 km) north-northeast of Agrihan.  Sanvu was moving toward the north-northeast at 3 m.p.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 994 mb.

Tropical Storm Sanvu developed when a distinct center of circulation formed within a much larger area of low pressure over the northern Marianas.  The circulation of Sanvu is still in the early stages of consolidation around the center.  Most of the showers and thunderstorms were forming in bands in the southern half of the circulation.  The bands in the northern half of the circulation were weaker.  The showers and thunderstorms south of the center were beginning to generate some upper level divergence which was pumping mass away to the south of the tropical storm.

Tropical Storm Sanvu will be moving through an environment that is somewhat favorable for intensification.  Sanvu will move over water where the Sea Surface Temperature is near 30.5°C.  Sanvu is under the axis of a narrow upper level ridge and the winds over the southern half of the circulation are fairly weak.  There is little vertical wind shear over that part of the tropical storm.  An upper level trough north of the ridge is producing stronger winds over that half of the circulation.  The stronger winds may be responsible for the lack of strong rainbands in the northern half of Sanvu.  The trough is forecast to move east and the shear in that region should decrease.  When the shear decreases Sanvu could intensify at a faster rate and it is forecast to become a typhoon in two or three days.

The trough is currently steering Tropical Storm Sanvu slowly toward the north-northeast.  When the trough moves away to the east a ridge if forecast to steer Sanvu more toward the north.  On its anticipated track Tropical Storm Sanvu will gradually move away from the northern Marianas and the weather should improve in that region.

Slow Moving Tropical Storm Harvey Causing Record Flooding in Texas

Slow moving Tropical Storm Harvey was causing record flooding in Houston and other places in southeast Texas.  At 2:00 p.m. EDT on Sunday the center of Tropical Storm Harvey was located at latitude 29.0°N and longitude 97.2°W which put it about 25 miles (40 km) northwest of Victoria, Texas.  Harvey was moving toward the southeast at 2 m.p.h. (3 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 was in effect for the portion of the coast from Port O’Connor to Sargent, Texas.

The center of Tropical Storm Harvey is drifting back toward the Gulf of Mexico.  A significant portion of the eastern side of Harvey is over water and the strongest winds are occurring in rainbands over the Gulf of Mexico.  Those winds are the reason Harvey is still a tropical storm and why there is still a tropical storm warning for a portion of the coast.  The circulation around Harvey is circulating over the water and it is transporting large amounts of moisture over southeast Texas.  Strong convergence into the center of Harvey is lifting the air and it is producing prolonged periods of heavy rain when rainbands move inland.

The extremely heavy rain in Harvey is causing record flooding in parts of Houston and other locations in southeastern Texas.  The Buffalo Bayou is currently at 67.46 feet (20.56 m).  The previous record water level was 61.2 feet (18.65 m).

The slow movement of Tropical Storm Harvey is exacerbating the flooding.  The winds are the steering level are weak and Harvey is now drifting back toward the southeast.  Harvey is drifting back over places it moved over on Saturday.  The center of Tropical Storm Harvey could drift back over the Gulf of Mexico.  If the center of Harvey moves back out over water, it would likely maintain its intensity.  Tropical Storm Harvey is forecast to continue to drop heavy rain over southeastern Texas and southwestern Louisiana during the next several days.

Tropical Storm Pakhar Makes Landfall Near Macau

Tropical Storm Pakhar sped across the South China Sea and made landfall on the coast of China near Macau.  At 11:00 p.m. EDT on Saturday the center of Tropical Storm Pakhar was located at latitude 22.3°N and longitude 112.7°E which put it about 60 miles (95 km) southwest of Hong Kong.  Pakhar was moving toward the northwest at 27 m.p.h. (43 km/h).  The maximum sustained wind speed was 65 m.p.h. (105 km/h) and there were wind gusts to 80 m.p.h. (130 km/h).  The minimum surface pressure was 987 mb.

Tropical Storm Pakhar will bring gusty winds and locally heavy rain as it quickly moves inland over southern China.  The wind and rain will hinder the efforts in the area to recover from Typhoon Hato.  Fortunately, Tropical Storm Pakhar is a fairly small storm.  Winds to tropical storm force only extend out about 80 miles (130 km) from the center of circulation.  The small size of Pakhar and its rapid rate of movement will limit the impact of the tropical storm.  Tropical Storm Pakhar should spin down fairly quickly as it rapidly moves inland.

Harvey Weakens to Tropical Storm, Still Dropping Heavy Rain on Texas

Hurricane Harvey weakened to a tropical storm on Saturday afternoon, but it was still dropping heavy rain on parts of Texas.  At 2:00 p.m. EDT on Saturday the center of Tropical Storm Harvey was located at latitude 29.1°N and longitude 97.6°W which put it about 45 miles (75 km) west-northwest of Victoria, Texas.  Harvey was moving toward the north-northwest at 2 m.p.h. (3 km/h).  The maximum sustained wind speed was 70 m.p.h. (110 km/h) and there were wind gusts to 85 m.p.h. (135 km/h).  The minimum surface pressure was 987 mb.

A Tropical Storm Warning was in effect for the portion of the coast from Baffin Bay to High Island, Texas.

The core of Hurricane Harvey moved inland over San Jose Island on Friday night.  It passed over Rockport, Texas and moved slowly north-northwest on Saturday.  The strongest wind occurred near Port Aransas, Rockport and Ingleside.  Some of the peak wind gusts were:

Port Aransas          132 m.p.h.   (213 km/h)

Copano Village       125 m.p.h.  (202 km/h)

Lamar                      110 m.p.h.  (177 km/h)

Rockport                 108 m.p.h.  (174 km/h)

Taft                            90 m.p.h.  (154 km/h)

Other than the fact that it is over land, Tropical Storm Harvey is in an environment favorable for a tropical cyclone.  The upper level winds are weak and there is little vertical wind shear.  Tropical Storm Harvey has weakened during the day, but it has maintained a very symmetrical structure.  Steady rain is falling in the core of the circulation and several bands of showers and thunderstorms in the outer portions of the circulation.  Tropical Storm Harvey has already produced heavy rain in some locations.  Some current rainfall totals are:

Aushell                   15.10″       (38 cm)

Coleto Creek         12.57″       (32 cm)

Richmond                9.60″       (24 cm)

Edna                       10.06″       (25 cm)

Danbury                  7.89″        (20 cm)

Sugarland               7.56″        (19 cm)

The steering winds are weak and Tropical Storm Harvey is forecast to make a slow counterclockwise loop during the next several days.  Since Harvey will not move very much, it will continue to rain in many of the same locations.  The potential for flooding will increase as the rain continues to fall.  Some rivers and streams could experience record flood levels.