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Hurricane Sandy Update: 5:00 PM EDT

By: louisianaboy444, 9:34 PM GMT on October 24, 2012

As of 320 pm EDT Hurricane Sandy was located around 17.9N 76.7W and is currently lashing Jamaica with hurricane conditions. Max sustained winds were 80mph with a centralized pressure of 973mb. Sandy is moving towards the north at around 12 kts due to cross-equatorial forcing from the monsoonal trough below and a trough located across the central Atlantic. This trough is helping to cause upper level shear of 60-70kts to the northeast of Sandy helping to ventilate her outflow.

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This water vapor imagery/Upper-Level wind overlay courtesy of CIMSS shows these features quite nicely

This trough is being deepened by a combination of the anticyclonic flow from the mid level high pressure system located over the eastern United States, outflow from Sandy and a jet max associated with a mid to upper level low pressure system near Nova Scotia. This graphic courtesy of NCAR shows these features well. This was from 12Z this morning ran out 12 hours to 00Z which is close to current time.

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You can see a jet max near California/Nevada helping to dig a trough across the central United States. You can also see a low pressure system in southern Canada that may very well be a player later in the forecast. You can also see the low near Nova Scotia with the associated jet max helping to dig this feature further.

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An anticyclone has formed over the center of Sandy although displaced slightly to the south which has brought upper level wind shear down to near 5-10 kts over her. The band of high shear to the north should move slowly to the east and should not affect her much near the Bahamas. As the mid- level high pressure system moves eastward upper level winds should be in the 10-20 kt range over her in the next 48 hours.

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These two graphis show the high pressure over the eastern United States quite well. Forcing from the trough digging into the central United States will eventually push this high further eastward. This high will then get squeezed between the central U.S. trough and the developing low pressure system over the northern Atlantic. That coupled with the southern flank being eroded by Sandy should weaken this high over the next 24 to 36 hours.

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This graphic is from the 12Z GFS and shows 850 mb winds 36 hours out. You can see Sandy making her close approach to Florida while the high moves northward and slowly begins to erode. This pattern could trap Sandy in a period of weak steering currents and could move erratically during this period. This low pressure system that will be moving into southeastern Canada should amplify enough as to lift Sandy northeastwards when a secondary trough should be able to lift her almost out to sea. Some of the models especially the Euro and the GFS show this trough becoming very strong. This trough then turns Sandy in a funky type loop back to the northwest towards New England. This would be a very interesting scenario and one that will have to be looked at closely. Right now I am leaning on the fact that the trough should move progressively taking Sandy out to sea with it. Based off of the forecast above I would not be surprised to see Sandy peak in the Bahamas at or near 90-95 mph. I am expecting 50-60 mph winds for SE florida and some higher waves being produced for the eastern seaboard. This forecast could change with future model runs.

Forecaster Sonnier

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Synoptic/Tropical Weather Update: October 2nd 2012

By: louisianaboy444, 11:11 PM GMT on October 02, 2012



Brief Tropical Update

Tropical Storm Nadine is still a churning in the Atlantic ocean. The numbers as of 5PM call it a tropical storm with 60mph winds. It is currently located at 34.4N 36.7W moving eastward. This means that the mid-latitude westerlies have finally captured this system and are bringing it to its demise.

Invest 96L

A strong tropical disturbance in the Central Atlantic located around 925 miles west of the Cape Verde Islands has garnered the attention of the National Hurricane Center. The NHC gives this system a 70% chance of development over the next 48 hours. An upper level anticyclone has formed over the system which is helping the storm have decent outflow on its northeastern quadrant.

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This GOES floater image shows the decent outflow of the storm on the northeastern quadrant with a squashed appearance on its western flank. This could be attributed to stiff southwesterly shear of 30-40 kts just ahead of the system.

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This wind shear analysis from the CIMSS data page shows the band of 30-40 kt shear. The culprit is a upper-level trough moving over the Northern Atlantic. This trough has amplified thanks in part to a big dome of high pressure that has developed off the Eastern seaboard.

This water vapor imagery shows our synoptic features nicely.

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You can clearly see the trough on the eastern side of the image. Following the upper level flow from the GOES Visible satellite, one can clearly see the direction Invest 96L will be steered. This long-wave trough is expected to lift this system out pretty quickly.
Dry air is also present over the Gulf of Mexico. This dry air is associated with shortwave ridging located over the Eastern Pacific. The anticyclonic motion of the ridge off the east coast coupled with cyclonic flow from a longwave trough located across Eastern Texas is creating a very potent jet max in the southeastern U.S. helping to usher in this dry air.

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This 250mb contour plot courtesy of UCAR shows this situation quite nicely, although this analysis was from 1200 UTC this morning. Because of this the Gulf of Mexico should be closed for business for some time. With the amount of mid-latitude westerlies starting to penetrate the gulf it is looking likely that the Gulf of Mexico season could be coming to a close in the next couple of weeks.

Water Vapor imagery depicting the dry air

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700mb analysis courtesy of UCAR depicts a shortwave near Louisiana but precipitation is not expected with drier air moving into the area. 850mb analysis also shows the low pressure associated with this weekend's storm has moved into the Ohio valley. With minimum forcing on its upper level energy, this storm system will be slow to move out but most models show the east coast clearing out over the next 24 hours.

This is my first analysis in awhile so forgive me for being rusty.

FORECASTER TREVOR

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