Tag Archives: Hurricane Michael

Jeff Masters on NE Weather, Leslie, Michael, & New Waves

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Severe weather in the Northeast U.S.; updates on 90L, 91L, Leslie and Michael
Published: 4:07 PM GMT on September 08, 2012

A significant severe weather outbreak is underway today across much of the Northeastern U.S., including metro New York City and Philadelphia. NOAA’s Storm Prediction Center has placed the region in their “Moderate Risk” area for severe weather. A fall-like low pressure system with a very powerful cold front will sweep through the region today, triggering widespread severe thunderstorms that may organize into a “derecho” event with damaging winds covering a large swath of the Northeast. A few tornadoes may accompany the event, and several tornado warnings have already been issued in New York, with a possible tornado touchdown in the Point Breeze section of the Rockaway peninsula in Queens. The same storm system killed four people on Friday in northeast Oklahoma; three of the deaths occurred when strong thunderstorms winds blew a mobile home into a ravine. Record heat was observed in advance of the storm’s cold front yesterday; Wichita Falls, TX hit a record high of 109, the hottest temperature ever recorded there so late in the season. When the cold front blew through at 7 pm CDT, the temperature dropped 15 degrees in 16 minutes, falling to 66 degrees by midnight. Wunderground meteorologist Shaun Tanner has more on the severe weather potential for the Northeast in his blog.


Figure 1. Severe weather potential for Saturday, September 8, 2012.

90L in the Gulf not a threat to develop
A partial remnant of Hurricane Isaac off the coast of the Florida Panhandle, Invest 90L, continues to be disrupted by wind shear, and no longer has time to develop before landfall occurs along the Florida Gulf Coast tonight or Sunday. Visible satellite loops show that 90L has a small area of poorly organized heavy thunderstorms, which will bring some areas of heavy rain to Florida today and Sunday.

Leslie still struggling with cool waters
Tropical Storm Leslie continues to feel the impact of the the cool waters it stirred up due to its long pause south of Bermuda, and remains a 65 mph tropical storm. The storm has no eyewall, as seen on satellite loops, but has cleared out a large cloud-free center. As Leslie continues to move north over warmer water, the storm should be able to build an eyewall and become at least a Category 1 hurricane. However, Leslie is expected to pass far enough to the east of Bermuda today and tonight that top winds of 45 mph will be observed on the island. Bermuda radar shows a large area of heavy rain from Leslie is very close to the island.


Figure 2. Morning radar image of Tropical Storm Leslie from the Bermuda radar.

Forecast for Leslie
The strong trough of low pressure pulling Leslie to the north will bring Leslie very close to Newfoundland, Canada by Tuesday night or Wednesday morning. At that time, Leslie should be weakening due to cooler waters and increased wind shear, and is likely to be a tropical storm. Heavy rain will be the main threat to Newfoundland. The latest 11 am EDT NHC wind probability forecast calls for a 24% chance that Leslie will be a Category 1 or stronger hurricane Wednesday morning at 8 am EDT, when the storm will be near Newfoundland. Even if the core of Leslie misses Newfoundland, the island will still likely experience tropical storm-force winds, since 39+ mph winds will probably extend outward from its center 180 miles to its west on Tuesday and Wednesday. Large swells from Leslie continue to pounding the entire Eastern Seaboard, and are creating beach erosion and dangerous rip currents.


Figure 3. Hurricane Michael as seen by NASA’s Aqua satellite at 11:50 am EDT Friday September 7, 2012. At the time, Michael was a Category 2 hurricane with 105 mph winds. Image credit: NASA.

Hurricane Michael weakens to Category 2
Hurricane Michael remains a Category 2 storm with 105 mph winds, out over the open mid-Atlantic Ocean. Satellite loops show that Michael is still an impressive storm with a well-developed eye. None of the models show that Michael will threaten any land areas during the coming five days, and Michael will likely die at sea over cold waters northeast of Newfoundland in 5 – 7 days.

91L off the coast of Africa
A tropical wave that emerged off the coast of Africa on Friday has been designated Invest 91L by NHC today. Most of the reliable computer models are predicting that 91L will develop into a tropical depression by Wednesday. None of the reliable computer models foresee that this storm will be a threat to the Lesser Antilles Islands, but it is still early to be assuming that 91L will recurve harmlessly out to sea.

Latest on Leslie & Michael fr/Dr. Jeff Masters

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90L in the Gulf disorganized; Leslie and Michael weaken
Published: 4:27 PM GMT on September 07, 2012

A partial remnant of Hurricane Isaac off the coast of Louisiana, Invest 90L, was almost torn apart last night by wind shear, but is making a bit of a comeback today. Visible satellite loops and surface observations from buoys and oil rigs in the Gulf show that 90L has an sloppy, elongated surface circulation. The area covered by heavy thunderstorms is relatively modest, and has been pushed to the south side of the circulation center by strong northerly winds that are creating a high 20 knots of wind shear. There is a large amount of dry air that surrounds 90L on all sides that is interfering with development. A hurricane hunter aircraft scheduled to investigate 90L today was cancelled, and has been rescheduled for Saturday afternoon.


Figure 1. Visible satellite image of Invest 90L taken at 11:58 am EDT Friday September 7, 2012.

Forecast for 90L
Wind shear over 90L is predicted to stay in the moderate to high range, 15 – 20 knots, through Saturday morning, then drop to the low range Saturday afternoon through Sunday. Ocean temperatures in the Gulf are 28.5° – 29°C, which is plenty warm enough to support formation of a tropical storm. 90L is essentially stationary this morning, but should begin a slow motion to the east-northeast tonight, in response to the steering flow from a trough of low pressure and its associated surface cold front approaching the Gulf Coast from the northwest. This trough should be capable of pulling 90L to a landfall along the Florida Panhandle or west coast of Florida by Sunday morning. In their 8 am Tropical Weather Outlook, NHC gave 90L a 20% chance of developing into a tropical depression by Sunday morning. I put these odds higher, at 30%.

Leslie weakens to a tropical storm
Tropical Storm Leslie continues to remain nearly stationary to the south of the island of Bermuda, and a NOAA hurricane hunter aircraft found this morning that Leslie had weakened below hurricane strength, to a 70 mph tropical storm. An ocean probe launched by the aircraft found that the ocean temperatures at one location in Leslie were 24.5°C, a full 5°C (8°F) drop from when the storm first reached the area two days ago. Moderate wind shear of 10 – 20 knots due to strong upper-level winds out of the west continue to drive dry air to Leslie’s west into the core of the storm. The combined effect of shear and cool waters have eroded away Leslie’s core, and the storm has no eyewall, as seen on satellite loops. A NOAA hurricane hunter aircraft will be in the storm tonight, and an uncrewed NASA Global Hawk aircraft finished an HS3 Hurricane Research Mission into Leslie this morning.


Figure 2. Hurricane Leslie as seen by NASA’s Aqua satellite at 10:45 am EDT Thursday, September 6, 2012. At the time, Leslie was a Category 1 hurricane with 75 mph winds. Image credit: NASA.

Forecast for Leslie
A strong trough of low pressure approaching the U.S. East Coast should make Leslie start moving to the north at 5 mph by Saturday morning. The models have stayed with their more eastwards solution to Leslie’s track, which keeps the threat of Bermuda receiving hurricane-force winds relatively low, since the island is expected to be on the weak (left) side of the storm. If the official NHC forecast verifies, tropical storm-force winds will just graze Bermuda Sunday morning through Sunday evening. According to the latest SHIPS model forecast, the shear is expected to fall to the low category, 5 – 10 knots, by Friday night. Leslie is over warm ocean waters of 29 – 30°C, and once the storm moves away from the large pool of cool waters it has stirred up, the reduction in shear and warm waters should allow the storm to intensify to at least a Category 1 hurricane by Sunday. The latest 11 am EDT NHC wind probability forecast calls for a 30% chance that Leslie will be a Category 2 or stronger hurricane Sunday morning at 8 am EDT, when the storm will be beginning its closest pass to Bermuda. Leslie is a huge storm, and tropical storm-force winds are expected to extend outward from its center 200 – 220 miles by Sunday.

Most of the models indicate Leslie is likely to make landfall in Newfoundland, Canada on Tuesday night or Wednesday morning. However, the models have been trending more to the east with Leslie’s track in recent runs, and given the uncertainty in 4-day hurricane forecasts, the storm could very well miss the island, passing to the northeast. Large swells from Leslie are pounding the entire Eastern Seaboard, and are creating beach erosion and dangerous rip currents.


Figure 3. Hurricane Michael as seen by NASA’s Aqua satellite at 12:20 pm EDT Thursday September 6, 2012. At the time, Michael was a Category 3 hurricane with 115 mph winds. Image credit: NASA.

Hurricane Michael weakens to Category 2
The only major hurricane of the 2012 Atlantic hurricane season, Hurricane Michael, has weakened, and is now a Category 2 storm with 105 mph winds. Satellite loops show that Michael is still an impressive storm with a well-developed eye, but the storm is not as symmetric, and the eye no longer as distinct as was the case yesterday. Michael is far out over the open Atlantic, and none of the models show that Michael will threaten any land areas during the coming seven days.

Elsewhere in the Atlantic
Most of the reliable computer models are predicting that a new tropical wave moving off the coast of Africa today will develop into a tropical depression by the middle of next week. This wave is predicted to exit Africa too far north to threaten the Lesser Antilles Islands.

from:    http://www.wunderground.com/blog/JeffMasters/article.html

Hurricanes and More Hurricanes

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Leslie near hurricane strength; Son of Isaac (90L) emerges in the Gulf
Published: 3:05 PM GMT on September 05, 2012

Tropical Storm Leslie is growing more organized and is approaching hurricane strength on its slow voyage northwards at 2 mph towards the island of Bermuda. Moderately high wind shear of 15 – 20 knots due to strong upper-level winds out of the northwest continues to keep most of Leslie’s heavy thunderstorms pushed to the east side of the storm, but satellite loops show that Leslie now has an impressive blow-up of heavy thunderstorms with cold cloud tops near its center. Leslie’s slow forward speed means that the storm is staying over the cold water stirred up by the storm’s winds, inhibiting intensification, but the waters underneath Leslie are warm to great depth, making this less of a factor than usual. According to the latest SHIPS model forecast, the shear is expected to fall steadily today, reaching the low category, 5 – 10 knots, by Thursday afternoon. Leslie is over warm ocean waters of 29 – 30°C, and the reduction in shear and warm waters should aid intensification, and potentially allow Leslie to be at Category 2 strength at its closest pass by Bermuda Saturday night and early Sunday morning, as indicated by the official NHC forecast. The latest 11 am EDT NHC wind probability forecast calls for a 48% chance that Leslie will be a Category 2 or stronger hurricane Sunday morning at 8 am EDT. Leslie is a huge storm, and tropical storm-force winds are expected to extend outward from its center 250 miles by Friday. Bermuda is likely to see a 42-hour period of tropical storm-force winds beginning Saturday morning near 2 am AST, and lasting until 8 pm AST Sunday night. The official NHC forecast shows Leslie nearly making a direct hit on Bermuda, and Leslie will be capable of bringing an extended period of hurricane-force winds lasting six or more hours to Bermuda Saturday night through Sunday morning, should a direct hit materialize. NHC is predicting that hurricane-force winds will extend outwards from the center of Leslie by 35 miles on Thursday night, and I expect this will increase to at least 60 miles by early Sunday morning, when Leslie will be making its closest pass by Bermuda.


Figure 1. Morning satellite image of Tropical Storm Leslie. Heavy thunderstorms have built near the center of the storm, and Leslie is near hurricane strength.

Leslie’s impact on Canada
Leslie will stay stuck in a weak steering current environment until a strong trough of low pressure approaches the U.S. East Coast on Saturday. The timing of this trough is such that Leslie will be pulled northwards and then north-northeastwards over the weekend. There are still significant differences among the models in the timing and speed of Leslie’s track over the weekend, but we can now dismiss the threat of Leslie making a direct hit on New England. The storm is likely to make landfall in Nova Scotia or Newfoundland, though there are significant differences in the models’ predictions of the timing of Leslie’s arrival in Canada. The GFS model predicts an early Tuesday landfall in Newfoundland, but the ECMWF model is much faster and farther west, predicting a Monday afternoon landfall in Nova Scotia. Large swells from Leslie are pounding the entire Eastern Seaboard, and these waves will increase in size as Leslie grows in strength this week. The Hurricane Hunters are scheduled to make their first flight into Leslie on Thursday afternoon.


Figure 2. Morning radar image of Invest 90L off the coast of the Florida Panhandle.

Son of Isaac: Invest 90L emerges in the Gulf of Mexico
During Tropical Depression Isaac’s trek across the center of the U.S. during the Labor Day weekend, the storm was ripped in half. One portion of the storm moved over the Northeast U.S., bringing heavy rains there, and another portion sank southwards over Alabama. You can see this split by studying an animation of the vorticity at 850 mb (the amount of spin at low levels of the atmosphere, near 5,000 feet above sea level) from the University of Wisconsin. This remnant of Isaac, which still maintained some of Isaac’s spin, brought heavy rains of 5 – 10 inches that caused flooding problems over portions of Alabama on Tuesday. The storm has now emerged over the Gulf of Mexico near the Florida Panhandle, and was designated Invest 90L this morning by NHC. In their 8 am Tropical Weather Outlook, NHC gave 90L a 20% chance of developing into a tropical depression by Friday morning. According to NHC naming rules, “if the remnant of a tropical cyclone redevelops into a tropical cyclone, it is assigned its original number or name”. Since “the remnant” refers to the primary remnant, and 90L does not fit the definition of a “primary remnant”, the storm will be given a new name should it develop into a tropical storm, according to information posted on the NHC Facebook page. Esau or Jacob–the names of the sons of the biblical Isaac–would be fitting names for 90L, but the next storm on the list of Atlantic storms is Nadine.

Long-range radar out of Mobile, Alabama shows a large area of heavy rainfall along the coast due to 90L. The echoes do show some spiral banding behavior, but there is only a slight evidence of rotation to the storm. Infrared satellite loops show that the thunderstorms associated with 90L are not that vigorous and do not have particularly cold cloud tops, and the area covered by the thunderstorms is relatively small. Wind shear is a high 20 – 30 knots over the northern Gulf of Mexico, but is predicted to fall to the moderate range, 10 – 20 knots, by Thursday afternoon. Ocean temperatures in the Gulf have been cooled down considerably by the passage of Hurricane Isaac last week, and are 28 – 28.5°C. This is still plenty warm enough to support formation of a tropical storm, and I expect 90L will increase in organization on Thursday and Friday as it moves slowly south or south-southwest. 90L could become a tropical depression as early as Thursday, though Friday is more likely. A hurricane hunter aircraft is scheduled to investigate 90L on Thursday afternoon. A trough of low pressure and an associated surface cold front will move southeastwards over the northern Gulf of Mexico on Sunday, and this trough should be capable of pulling 90L to the northeast to a landfall along the Florida Panhandle or west coast of Florida on Sunday.


Figure 3. Morning satellite image of Tropical Storm Michael.

Tropical Storm Michael in the Central Atlantic
Tropical Storm Michael has strengthened to 50 mph winds, and appears to have a favorable enough environment to become a hurricane later this week. Satellite loops show that this is a small tropical cyclone, far out over the open Atlantic, and none of the models show that Michael will threaten any land areas.

Elsewhere in the Atlantic
The GFS and ECMWF models are predicting that a new tropical wave due to move off the coast of Africa on Friday will develop into a tropical depression by the middle of next week. It’s too early to tell if this system might threaten the Lesser Antilles Islands.

from:    http://www.wunderground.com/blog/JeffMasters/article.html