Tropical weather analysis - September 30, 2012

By: KoritheMan , 7:37 AM GMT on September 30, 2012

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Nadine

Nadine is one tenacious bugger. As of the latest NHC advisory, the storm actually strengthened a little:

Wind: 85 mph, with higher gusts
Location: 35.6°N 37.5°W
Movement: NNW at 10 mph
Pressure: 984 mb
Category: 1 (Saffir-Simpson Hurricane Scale)

Satellite images suggest that the eye has become better defined over the last few hours, although cloud tops in the eyewall have warmed a bit.



Figure 1. Latest infrared satellite image of Hurricane Nadine. Image credit: NOAA

There really isn't any real evidence of vertical shear over Nadine, or in the nearby storm environment. Nor do I see many downstream features that would be capable of causing a sudden spike in wind shear over the hurricane. Indeed, it looks as if the upper tropospheric flow, barring subtle upper level changes due to alternating passages of shortwaves -- troughs and ridges -- I don't really expect an appreciable increase in shear until about 72 hours. Beyond that time, an increase in southerly shear is forecast as Nadine interacts with a rather strong baroclinic zone over the north Atlantic.

It should be noted that Nadine's current operational intensity of 75 kt is the same as its initial peak two weeks ago. This is somewhat remarkable considering that the cyclone has been over sub-26C SSTs for about 36 hours. I initially did not expect this given that there appeared to be more ridging than troughing over the subtropics, but a similar synoptic situation that allowed Chris to become a hurricane over cool waters all the way back in June appears to have set up again for Nadine. AMSU temperature cross section diagrams from yesterday (Saturday) revealed that the upper troposphere is rather cold. Hence, it appears that the relative temperature gradient between the lukewarm sea surface temperatures and the rather cold upper-level temperatures are providing the mechanisms for intensification with Nadine, in an environment not generally considered conducive for tropical cyclone formation and intensification. It is a little uncertain how long this upper support can continue, but I suspect for at least the next 36 hours.

Gradual weakening is expected beyond 36 hours, although it should be noted that with the expectation of lower vertical shear through 72 hours, any subtle environmental change -- namely one akin to the one being experienced now, with cold temperatures aloft relative to warm water temperatures -- could allow the hurricane to remain stronger than indicated below. Also, I have kept the 96 and 120 hour intensities up a little, as I see a strong likelihood of the north Atlantic low giving Nadine a burst of baroclinic forcing.

Regardless, Nadine is forecast to become extratropical at the end of the forecast period as it interacts with a large mid- to upper-level trough over the north Atlantic. The global models are in good agreement with this, and for the sake of my own sanity, I sincerely hope they are correct.

The steering for Nadine remains a little complex, at least in the short-term. Water vapor imagery shows a mid- to upper-level trough passing to the north of the hurricane. This would coincide well with the uniform zonal (west to east) flow north of about 35N. Downstream and closer to home, another trough with its parent upper low over the Ohio Valley, appears to be slowly amplifying over the western Atlantic waters. This appears to be the trough that should ultimately cause Nadine to lose tropical characteristics as well as accelerate her out of the subtropics. However, this developing system is not moving much at the moment, and will likely gain little latitude over the next day or two. After that time, model guidance is unanimous in bringing the system into the north Atlantic, which should increase the southerly flow over Nadine and cause a gradual acceleration.

The models continue to show a tight cyclonic loop over the next 24-48 hours as surrounding steering currents collapse. This is supported by current observational trends, as the zonal flow over the north Atlantic suggests that the shortwave to the north will bypass Nadine. I will show a southward motion as well, but not as much as most of the guidance.

5-day intensity forecast

INITIAL 09/30 0900Z 75 KT 85 MPH
12 hour 09/30 1800Z 75 KT 85 MPH
24 hour 10/01 0600Z 75 KT 85 MPH
36 hour 10/01 1800Z 75 KT 85 MPH
48 hour 10/02 0600Z 70 KT 80 MPH
72 hour 10/03 0600Z 65 KT 75 MPH
96 hour 10/04 0600Z 55 KT 65 MPH
120 hour 10/05 0600Z 55 KT 65 MPH...POST-TROPICAL/EXTRATROPICAL

5-day track forecast



Figure 2. My 5-day forecast track for Nadine.

With a total of nearly 18 days as a tropical cyclone, Nadine has become the longest-lasting Atlantic hurricane since Hurricane Bertha in 2008.



Jelawat

I will not have a post on Jelawat tonight, as it is poised to make landfall in southern Japan soon, accelerating in mid-latitude southwesterly flow. Strong winds may impact the Tokyo metropolitan area, which may produce some sporadic power outages. Rainfall will be quite limited, especially in the southern and western quadrants of the storm, which appear to be entraining dry air. This is consistent with extratropical transition, which is likely to occur in about a day or so.



Elsewhere

None of the computer models are showing anything remotely suggestive of a tropical threat in the Atlantic for the next seven days. The rainy low pressure system over the northern Gulf Coast is expected to remain inland, and development is no longer feasible.

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3. WunderAlertBot (Admin)
12:51 AM GMT on October 02, 2012
KoritheMan has created a new entry.
2. wxchaser97
11:11 AM GMT on September 30, 2012
Thanks Kori, Nadine is now up to 90mph.
Member Since: March 16, 2012 Posts: 127 Comments: 7928
1. SherwoodSpirit
9:18 AM GMT on September 30, 2012
"... for the sake of my own sanity, I sincerely hope they are correct."
hehe
Nadine drivin' ya a little batty?
Member Since: July 18, 2006 Posts: 0 Comments: 394

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About KoritheMan

I'm just a 23 year old with an ardent passion for weather. I first became aware of this interest after Tropical Storm Isidore struck my area in 2002.