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Tropical weather analysis - September 23, 2012

By: KoritheMan , 7:04 AM GMT on September 23, 2012

Remnants of Nadine

Satellite images and surface observations suggest that the area of low pressure associated with former Hurricane Nadine is becoming better organized. Earlier microwave data suggested the presence of a well-defined, albeit exposed circulation. Since those passes, convection has increased in both coverage and extent, and a curved band is prominent north of the center. All it would take is detachment from the front and the system could probably be considered tropical. The global models suggest this will happen soon, and water vapor imagery supports it as well, as the parent upper low moves off toward Europe.

The low is expected to moves slowly westward over the next day or two.



Figure 1. Latest infrared satellite image of ex-Nadine. Image credit: RAMMB Colorado State University (CSU).

Probability of development in 48 hours: 70%



Miriam

Tropical Storm Miriam is intensifying as of the latest NHC advisory:

Wind: 45 mph, with higher gusts
Location: 14.9°N 108.5°W
Movement: WNW at 8 mph
Pressure: 1002 mb



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

Conditions appear conducive for additional strengthening. The shear should remain low for the next 48-72 hours. In fact, the only apparent hurdle I see that would prevent Miriam from becoming a major hurricane is a tongue of cooler waters that lie west of 115W. Given the extremely favorable environmental conditions that lie ahead, my intensity forecast is a little higher than the intensity consensus. It is possible that Miriam could get a little stronger than anticipated. Beyond 48 hours, a weakening trend is expected to initiate as the cyclone encounters cooler waters, drier air, and increasing southwesterly shear.

Miriam is situated on the southwest periphery of a well-established low- to mid-level ridge over the southwestern United States. This should continue the current west-northwest motion for about the next 72 hours. After that time, there is a significant divergence in the model guidance, which since seems to hinge primarily on how strong Miriam is, as well as the amplitude of the upper trough now amplifying off the coast of the western United States. The GFS continues to call for an eventual landfall on the coast of western or central Baja, and has shifted southward in the 0z run. The ECMWF shows a westward motion beyond 72 hours as the trough lifts out. Since it is impossible to pinpoint the strength of the trough and Miriam's depth at this point in time, the best course of action seems to be an average of the extremes. That leads to a northwestward bend beyond day three under the assumption that Miriam feels the trough, but not to the extent that it recurves. This is a low confidence forecast.

I am similar to that from the National Hurricane Center for lack of a reason to disagree with it.

5-day intensity forecast

INITIAL 09/23 0600Z 40 KT 45 MPH
12 hour 09/23 1800Z 50 KT 60 MPH
24 hour 09/24 0600Z 60 KT 70 MPH
36 hour 09/24 1800Z 70 KT 80 MPH
48 hour 09/25 0600Z 80 KT 90 MPH
72 hour 09/26 0600Z 70 KT 80 MPH
96 hour 09/27 0600Z 60 KT 70 MPH
120 hour 09/28 0600Z 45 KT 50 MPH

5-day track forecast



Figure 3. My 5-day forecast track for Miriam.



Jelawat

I don't normally blog for western Pacific systems, but Typhoon Jelawat is simply too marvelous to pass up. As of the latest advisory from the Joint Typhoon Warning Center (JTWC), the following information was available on the typhoon:

Wind: 115 mph, with higher gusts
Location: 12.2N 128.9E
Movement: Stationary



Figure 4. Latest infrared satellite image of Typhoon Jelawat. Image credit: NOAA

The satellite signature is nothing short of impressive. Very deep convection wraps around a well-defined eye, and numerous rainbands are emanating from the cyclone.

Environmental conditions ahead of the typhoon appear favorable for strengthening. Since Jelawat has been rapidly intensifying, with Dvorak numbers rising as fast as constraints allow, it has the potential to become a super typhoon, and possibly a Category 5 equivalent on the Saffir-Simpson Hurricane Scale. The Western Pacific is home to a vast reservoir of deep warm water, and it is not uncommon to see storms with winds over 140 mph on a regular basis here. Beyond 72 hours, an increase in southwesterly shear is likely as the system moves closer to an upper-level trough.

An upper trough near the north coast of Japan is pivoting eastward in the mid-latitude westerly flow over mainland China. While the main trough is moving generally eastward, there is apparently enough northwesterly flow along the back side of the parent upper low to help push the southern portion of the frontal trough southward, closer to the vicinity of the tropical cyclone. This is allowing for a small break in the ridge to the north of the storm, which is also depicted on UW-CIMSS steering imagery. The net result should be a bend to the north later today. I don't disagree too strongly with the current JTWC track for the first couple of days, although I'm not going to show the strong northwestward bend that they are showing, since there appears to be a ton of shortwave energy over China coming out of the westerlies. This could theoretically help to reinforce the large-scale troughiness in this region.

Next week, this system is expected to threaten Okinawa and possibly mainland Japan.

5-day intensity forecast

INITIAL 09/23 0900Z 100 KT 115 MPH
12 hour 09/23 1800Z 105 KT 120 MPH
24 hour 09/24 0600Z 110 KT 130 MPH
36 hour 09/24 1800Z 115 KT 135 MPH
48 hour 09/25 0600Z 125 KT 145 MPH
72 hour 09/26 0600Z 125 KT 145 MPH
96 hour 09/27 0600Z 105 KT 120 MPH
120 hour 09/28 0600Z 90 KT 105 MPH

Unfortunately, I could not find a map with which to draw track forecasts on. However, my track is basically for a general northward motion for the next three to four days, followed by recurvature toward the northeast.


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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8. GeorgiaStormz
2:05 PM GMT on September 23, 2012
Tha Blog Is Hot.
Member Since: December 31, 1969 Posts: Comments:
7. GeorgiaStormz
2:03 PM GMT on September 23, 2012
Tha Blog Is Hot.
Member Since: December 31, 1969 Posts: Comments:
6. wxchaser97
10:18 AM GMT on September 23, 2012
Thanks Kori, Jelawat is one impressive typhoon.
Member Since: December 31, 1969 Posts: Comments:
5. pcola57
9:20 AM GMT on September 23, 2012
Well done Kori..
Jelwat is very impressive for sure..
Thanks for your input.
Member Since: December 31, 1969 Posts: Comments:
4. KoritheMan
8:49 AM GMT on September 23, 2012
Quoting HadesGodWyvern:
that 115 knots in 72 hours is a 7.5 (155 knots) on the Dvorak scale from the JMA.

DANG!


155 knots would be what, exactly? Don't really feel like calculating, lol.
Member Since: December 31, 1969 Posts: Comments:
3. HadesGodWyvern (Mod)
7:50 AM GMT on September 23, 2012
that 115 knots in 72 hours is a 7.5 (155 knots) on the Dvorak scale from the JMA.

DANG!
Member Since: December 31, 1969 Posts: Comments:
2. HadesGodWyvern (Mod)
7:49 AM GMT on September 23, 2012
** wtpq30 rjtd 230600 ***

Rsmc tropical cyclone prognostic reasoning
Reasoning no. 7 for ty 1217 jelawat (1217)
1.General comments
Reasoning of prognosis this time is similar to previous one.
Position forecast is mainly based on nwp and persistency.
2.Synoptic situation
Nothing particular to explain.
3.Motion forecast
Position accuracy at 230600 utc is good.
Ty will accelerate for the next 24 hours.
Ty will move north for the next 72 hours.
4.Intensity forecast
Fi-number will be 7.0 after 24 hours.=


----
another Category five forecast.
Member Since: December 31, 1969 Posts: Comments:
1. AussieStorm
7:22 AM GMT on September 23, 2012
Nice!!
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Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.

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