Tropical weather analysis - August 30, 2012

By: KoritheMan , 12:57 AM GMT on August 31, 2012

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Kirk

I've been neglecting to mention it because of personal impacts from Isaac to my area, but former 97L became Kirk a couple days ago. Since that time, Kirk has quickly become a hurricane. As of the latest NHC advisory, the following has been posted on this storm:

Wind: 90 mph, with higher gusts
Location: 28.2°N 50.3°W
Movement: NNW at 13 mph
Pressure: 982 mb
Category: 1 (Saffir-Simpson Hurricane Scale)

Kirk is a small but well-organized hurricane, with a small eye embedded in the central dense overcast. There is some banding to the north, and the outflow pattern is well-established in all but the southern quadrant.



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

There is some dry air in the near-storm environment. Since Kirk is a very small hurricane, it will be more prone than usual to subtle changes in the atmosphere. However, Kirk seems to have done fairly well for itself in terms of warding off any dry air. Given current trends, Kirk may be rapidly intensifying, and the cyclone is expected to become a major hurricane in about 24 hours, but it could occur sooner. Barring any dry air entrainment, which should be largely mitigated by the hurricane's acceleration, conditions appear favorable for continued strengthening until around 48 hours, at which point Kirk is forecast to lose its anticyclone, begin moving over cooler waters and into an environment of very strong southwesterly shear. The conglomeration of these factors should bring about weakening at those times. The global models suggest that Kirk will become extratropical in about four days, and become absorbed by a frontal zone thereafter.

Recent satellite fixes suggest that Kirk has turned to the north around the western periphery of the subtropical ridge over the central Atlantic as a deep-layer trough approaches the hurricane from the west. A gradual bend to the northeast with some acceleration is forecast as the small hurricane becomes fully embedded in the trough. The model consensus is in excellent agreement on this scenario, and the synoptic pattern over this part of the Atlantic is rather straightforward.

5-day intensity forecast

INITIAL 08/31 0000Z 80 KT 90 MPH
12 hour 08/31 1200Z 90 KT 105 MPH
24 hour 09/01 0000Z 100 KT 115 MPH
36 hour 09/01 1200Z 105 KT 120 MPH
48 hour 09/02 0000Z 100 KT 115 MPH
72 hour 09/03 0000Z 75 KT 85 MPH
96 hour 09/04 0000Z 50 KT 60 MPH...EXTRATROPICAL
120 hour 09/05 0000Z...ABSORBED BY FRONTAL ZONE



Leslie

Tropical Storm Leslie formed earlier today from a strong tropical wave. As of the latest NHC advisory, the following was posted on the tropical storm:

Wind: 45 mph, with higher gusts
Location: 14.4°N 45.3°W
Movement: W at 21 mph
Pressure: 1004 mb

Satellite images show that Leslie is a well-organized tropical storm, with a ball of very cold convection near the low-level center. In addition, a well-defined curved band is seen emanating to the west of the center.



Figure 2. Latest infrared satellite image of Tropical Storm Leslie. Image credit: NOAA

Earlier microwave data suggested that the low-level center was along the northeast edge of the convection. Since that time, Leslie's satellite signature has improved, but the deepest convection still appears to be just south of the low-level center. This is probably due to a little bit of easterly shear associated with the storm relative anticyclone, which appears to be slightly dislodged from Leslie. However, the GFS forecasts a very favorable upper-level environment ahead of the storm, and the anticyclone in the 200 mb upper wind forecast from that model look almost as large as the one that eventually manifested over Hurricane Isaac. In addition, Leslie is large enough that it should be better shielded against the dry air over the central Atlantic than Kirk is. In fact, the SHIPS and HWRF actually forecast Leslie to become a major hurricane by the end of the forecast period. Lacking any obvious reason to suggest otherwise, I will indicate this as well.

Leslie is south of the subtropical ridge, which appears to be rebuilding in the wake of accelerating Hurricane Kirk. However, Leslie is moving quick enough that it should feel the residual weakness left behind by Kirk and a trough amplifying over the central Atlantic. The cyclone should respond by turning west-northwestward over the next 12-24 hours, followed by slowly by recurvature into the mid-latitude westerlies. The model consensus is in good agreement on this, although the ECMWF suggests that Leslie could stall near the end of the forecast period as a shortwave trough bypasses it and a ridge begins to rebuild. However, that model shows another shortwave moving into the western Atlantic almost immediately subsequent to the stall, which would favor recurvature like the remainder of the models are suggesting. In addition, an upper low is forecast to develop near the Bahamas soon from the trough that is recurving Kirk. This low is forecast to be strong from 500-300 mb, which should help to keep a continued poleward component on Leslie. However, if the storm does not move too far to the north over the next couple of days, it may pose a long-range threat to the northern Leeward Islands. I consider this to be a remote possibility at the moment, and the odds of it happening are only about 5%. Due to the uncertainty in long-range forecast tracks, interests in Bermuda should monitor the progress of Leslie.

5-day intensity forecast

INITIAL 08/31 0000Z 40 KT 45 MPH
12 hour 08/31 1200Z 45 KT 50 MPH
24 hour 09/01 0000Z 55 KT 65 MPH
36 hour 09/01 1200Z 60 KT 70 MPH
48 hour 09/02 0000Z 70 KT 80 MPH
72 hour 09/03 0000Z 80 KT 90 MPH
96 hour 09/04 0000Z 90 KT 105 MPH
120 hour 09/05 0000Z 100 KT 115 MPH



Ileana

Hurricane Ileana is moving across the open waters of the Eastern Pacific. As of the latest NHC advisory, the following was posted on the hurricane:

Wind: 85 mph, with higher gusts
Location: 20.5°N 114.1°W
Movement: NW at 6 mph
Pressure: 979 mb
Category: 1 (Saffir-Simpson Hurricane Scale)

Earlier microwave data revealed that the hurricane maintains an impressive inner core, with a well-defined eye. An eye is not evident on conventional imagery, and the hurricane is slowly losing organization.



Figure 3. Latest infrared satellite image of Hurricane Ileana. Image credit: NOAA

While upper-level winds are forecast to remain favorable, AOML SST analyses show that the hurricane is approaching the 26C isotherm, which in coordination with a very stable airmass should result in weakening, which appears to already be underway. Ileana is forecast to become a remnant low in about three days.

Ileana remains south of a weak mid-level ridge. Consequently, the hurricane is moving northwest. While the track is fairly straightforward, there is some disagreement between the GFS and ECMWF after 48 hours. The former suggests that Ileana will recurve ahead of the trough, while the latter indicates that the system will move westward in the low-level flow. Given the unfavorable environment, which tends to quickly weaken tropical cyclones in this part of the Pacific, I will side with the ECMWF. In any case, it seems to be of little consequence, as the hurricane should be a remnant low by that time. I am in agreement with the National Hurricane Center forecast track.

5-day intensity forecast

INITIAL 08/31 0000Z 75 KT 85 MPH
12 hour 08/31 1200Z 65 KT 75 MPH
24 hour 09/01 0000Z 55 KT 65 MPH
36 hour 09/01 1200Z 45 KT 50 MPH
48 hour 09/02 0000Z 35 KT 40 MPH
72 hour 09/03 0000Z 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
96 hour 09/04 0000Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
120 hour 09/05 0000Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW



Eastern Pacific disturbance

An area of disturbed weather located several hundred miles south of the Mexican coastline is currently disorganized. However, environmental conditions appear favorable for gradual development as it moves west-northwest at about 15 mph.

Probability of development in 48 hours: 30%

I will not be drawing track forecasts this evening, as I am staying over my dad's until the power comes back on at my residence. The whole family is here, which makes concentrating fully rather difficult. I will return to doing that when the power resumes where I live.

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3. TropicalAnalystwx13
1:44 AM GMT on August 31, 2012
Thanks Kori.
Member Since: July 6, 2010 Posts: 113 Comments: 32707
2. Thrawst
1:26 AM GMT on August 31, 2012
Thanks Kori!
Member Since: July 18, 2010 Posts: 50 Comments: 1909
1. MAweatherboy1
1:02 AM GMT on August 31, 2012
Thanks Kori, good to see you here, hope all goes well with the recovery down there.
Member Since: February 11, 2012 Posts: 84 Comments: 8001

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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.