Tropical weather analysis - October 1, 2011

By: KoritheMan , 4:51 AM GMT on October 02, 2011

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Ophelia

Hurricane Ophelia intensified into a Category 4 hurricane today as it was passing east of Bermuda. As of the latest NHC advisory, here is the information on the powerful hurricane:

Wind: 140 mph, with higher gusts
Location: 33.8°N 62.2°W
Movement: N at 26 mph
Pressure: 940 mb
Category: 4 (Saffir-Simpson Hurricane Scale)

While Ophelia intensified a little more than I had in mind, I noted in my previous forecast that intensification to major hurricane strength was possible. It is not unusual, historically, for tropical cyclones to quickly intensify when they interact with an approaching trough. This has been the case with several such storms in recent years, including but not limited to: Isaac and Michael of 2000, and Charley of 2004. Satellite loops show a formidable, respectable hurricane, with a large eye surrounded by intense convection within the eyewall. In fact, Ophelia is sporting a greater satellite presentation than Irene or Katia ever did.



Figure 1. Latest infrared satellite image of Hurricane Ophelia, courtesy of NOAA's Satellite Services Division (SSD).

Modest southwesterly shear is preventing appreciable outflow on Ophelia's southwest side. However, the normally negative impact of said shear is usually negligible for accelerating hurricanes. No, the main killer for Ophelia will be the cooling sea surface temperatures along the projected forecast track. By early Monday morning, the hurricane will cross the 26C isotherm; thereafter, SSTs fall sharply. That, combined with increasing southwesterly to westerly shear associated with a deep-layer trough, should act to quickly weaken the storm. This highly baroclinic environment should cause Ophelia to transition to a powerful extratropical low in about 48 hours. Ophelia has probably peaked in intensity.

Water vapor imagery reveals that Ophelia is accelerating northward ahead of fast southerly flow associated with the aforementioned trough. Global models forecast the hurricane to move north-northeast over the next 12-24 hours as southwesterly flow increases. It should be noted that all of the global models, with the exception of the ECMWF, bring Ophelia ashore extreme southeastern Newfoundland early Monday morning between 2 AM (eastern time) and sunrise. However, vertical shear will probably keep the majority of the precipitation confined downstream of the low-level center (and thus over water), as alluded to by the National Hurricane Center's most recent discussion. This should minimize rainfall potential, especially considering what would ordinarily be expected for a northeastward-moving system. Additionally, the relative lack of convection expected near the center at this time should keep also help to quell the wind threat, although locally strong winds, especially in gusts, could still occur near and to the east of where the center comes ashore. I am in pretty good agreement with the NHC official forecast track:



Figure 2. Latest NHC 5-day forecast track for Hurricane Ophelia.

A tropical storm watch has been posted for the Avalon Peninsula of Newfoundland. Should any deviation to the left of the expected track occur, tropical storm warnings could be required for that area by the hurricane center.

Philippe

Tropical Storm Philippe unexpectedly intensified today, despite continued northwesterly shear from his big sister Ophelia. As usual, this highlights our obvious lack of skill in making intensity forecasts. As of the latest NHC advisory, here were the coordinates on Philippe:

Wind: 70 mph, with higher gusts
Location: 25.4°N 49.8°W
Movement: WNW at 9 mph
Pressure: 996 mb
Category: Tropical storm (Saffir-Simpson Hurricane Scale)

Although scatterometer scans really don't lie, Philippe's structure is certainly not impressive. The convection is deep, but lacks curvature. Also, the center is somewhat exposed along the northwest edge of the thunderstorms.



Figure 3. Latest infrared satellite image of Tropical Storm Philippe, courtesy of NOAA's Satellite Services Division (SSD).

Philippe has about another three days of unfavorable shear before a narrow window of opportunity for intensification presents itself. Since Philippe has been a resilient tropical cyclone, I think it will survive the current hostilities, and then reintensify slightly later in the forecast period. My own intensity forecast is in excellent agreement with the NHC's:

INIT 02/0300Z 25.4N 49.8W 60 KT 70 MPH
12H 02/1200Z 25.8N 51.3W 55 KT 65 MPH
24H 03/0000Z 26.0N 53.4W 50 KT 60 MPH
36H 03/1200Z 25.9N 55.6W 45 KT 50 MPH
48H 04/0000Z 25.8N 57.8W 45 KT 50 MPH
72H 05/0000Z 26.5N 61.0W 45 KT 50 MPH
96H 06/0000Z 28.0N 61.0W 50 KT 60 MPH
120H 07/0000Z 31.5N 57.0W 55 KT 65 MPH

Philippe is beginning to feel the westward tug from the subtropical ridge, as evidenced by the current west-northwest movement given by the hurricane center. Global models forecast this feature to restrengthen in the wake of Ophelia, which should force Philippe on a westward track over the next couple of days. However, a large trough is forecast to ultimately cause Philippe to recurve well east of the United States. Climatology also favors this scenario. In general, the models forecast Philippe to begin recurving on Tuesday. The exception continues to be the GFS, which insists on moving Philippe very slowly, presumably due to a weaker depiction of the trough. This is considered unlikely for now, although given its bullishness in regards to this potential scenario, I agree with the NHC that it is best to forecast a slow motion during the onset of recurvature as a course of least regret.

Philippe might be a threat to Bermuda in about five days, but current indications are that, like Ophelia, the cyclone will pass well to the east.

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6. traumaboyy
12:30 AM GMT on October 03, 2011
Thanks Kori!!
Member Since: August 18, 2008 Posts: 0 Comments: 2266
5. KoritheMan
11:22 PM GMT on October 02, 2011
Quoting aspectre:
Is Phillipe supposed to fall into Ophelia's wake trough?
Or is the trough you mentioned a different critter altogether?


I believe it's a different entity altogether, because the ridge has rebuilt to the north.
Member Since: March 7, 2007 Posts: 603 Comments: 21829
4. HondosGirl
3:46 PM GMT on October 02, 2011
Your update was very clear and easy to understand for a newbie like me. Thanks for the update!
Member Since: August 20, 2011 Posts: 0 Comments: 111
3. aspectre
2:55 PM GMT on October 02, 2011
Is Phillipe supposed to fall into Ophelia's wake trough?
Or is the trough you mentioned a different critter altogether?
Member Since: August 21, 2007 Posts: 0 Comments: 4860
2. pcola57
5:16 AM GMT on October 02, 2011
Thanks for posting, very good update KoritheMan..
Hope no one is injured by this storm..
Keep posting your blog as I ,as I'm sure others do , find it interesting and clear put.
Thanks again..
Member Since: August 13, 2009 Posts: 13 Comments: 6927
1. HurricaneDean07
5:03 AM GMT on October 02, 2011
Great post. It will be Interesting to see how Philippe turns out. G'nite SO TIRED...
Member Since: October 3, 2010 Posts: 40 Comments: 4129

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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.

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