Tropical weather analysis - October 3, 2013

By: KoritheMan , 7:43 AM GMT on October 03, 2013


Jerry is slowly decaying over the central Atlantic. As of the 0300Z NHC advisory, the following information was posted on the storm:

Wind: 35 mph, with higher gusts
Location: 29.7°N 42.0°W
Movement: NE at 7 mph
Pressure: 1010 mb

Satellite estimates have fallen below tropical storm strength, and there is an absence of deep convection near the center. The nearest deep convection is about 100 miles east of the center in a disorganized storm cluster. If present trends continue, Jerry could degenerate into a remnant low sometime today. Given that convection has not returned during the diurnal maximum period, this is a distinct possibility.

Figure 1. Latest infrared satellite image of Tropical Depression Jerry. Image credit: NOAA's Satellite Services Division (SSD).

My forecast generously lets Jerry live for another 48 hours, but it could dissipate before then. The global models are starting to show the storm having less longevity, so I did not draw a forecast point beyond 72 hours with this forecast package.

Jerry is moving northeast as it feels the influence of a deep-layer trough to the west. The models continue to suggest it could pass near or over the Azores in a few days, but there is likely to be very little left of the cyclone by that time. My forecast track is similar to the current NHC prediction.

Intensity forecast and positions

INITIAL 10/03 0300Z 29.7°N 42.0°W 30 KT 35 MPH
12 hour 10/03 1200Z 30.3°N 41.1°W 30 KT 35 MPH
24 hour 10/04 0000Z 31.4°N 38.9°W 30 KT 35 MPH
36 hour 10/04 1200Z 32.5°N 36.3°W 30 KT 35 MPH
48 hour 10/05 0000Z 34.6°N 34.4°W 30 KT 35 MPH
72 hour 10/06 0000Z 35.4°N 31.3°W 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
96 hour 10/07 0000Z...DISSIPATED

Track forecast

Figure 2. My forecast track for Jerry.

Invest 97L

A well-defined area of low pressure located just east of the northeastern tip of the Yucatan Peninsula has continued to become better organized. It has the look of a developing tropical storm, and the 6z update from ATCF placed the maximum winds at 40 kt; hence, if classification happens overnight, there will be an immediate upgrade to a tropical storm. Surface observations from the Yucatan Peninsula suggest that a broad closed surface circulation may exist.

Figure 3. Latest infrared satellite image of Invest 97L. Image credit: NOAA's Satellite Services Division (SSD).

It has not been easy for me to locate the center this evening, but with the help of a fortuitous ASCAT pass, microwave comparisons, and radar data from Cancun, the low-level center appears to be located along the western edge of the convective cloud shield, which suggests the storm is struggling with westerly shear. Given the outflow pattern observed on water vapor imagery, any such shear is likely confined below the outflow layer. This shear is not expected to be enough to prohibit gradual strengthening of the disturbance over at least the next 48 hours. Beyond that time, the GFS suggests that westerly to southwesterly upper shear will increase as the system nears the northern Gulf Coast, which should curb any additional development, and may even cause the system to weaken somewhat before US landfall.

One possibility I was concerned about earlier in the day was that the system may develop an anticyclone before reaching the northern Gulf. If that were to verify, it would likely shunt the strongest shear to the north of the system, and allow it to potentially strengthen more than forecast. The outflow pattern is suggestive that the system has at least a weak anticyclone aloft, but it will remain to be seen how long the system can keep that.

Based on the upper-level wind parameters shown by the GFS, and the subsident airmass seen over the Gulf of Mexico on water vapor images, I am not currently anticipating a hurricane. However, there remains a very small chance, about 10%, that this could occur if the situation I described above with the anticyclone occurs.

Speaking of difficulty, it's been even harder to distinguish and determine the general motion of the system lacking recent reconnaissance observations and a reliable center fix via satellite imagery. With the help of a couple of decent microwave passes, my best guess is that the system is still moving northwestward. Water vapor and upper air data over the southern United States show a broad trough covers much of the central and southern United States, while a mid-level ridge exists downstream over the eastern United States coast and western Atlantic Ocean. This pattern suggests that the disturbance should continue moving northwestward to north-northwestward, followed by an eventual turn to the north as it approaches the northern Gulf Coast. While the models are in general agreement on the northward turn, there are substantial differences on where it will occur. The ECMWF and UKMET, likely at least partially in response to a weaker vortex, show the disturbance making landfall in southeastern Louisiana Saturday evening. On the other hand, the stronger GFS solution shows the system turning toward the Florida panhandle. Given development trends, the GFS solution automatically has more weight, but the ECMWF has been historically reliable. In addition, the majority of GFS ensemble members are considerably west of the operational run, which suggests that the westward turn shown by the ECMWF may not be completely unwarranted.

Looking at it carefully, the biggest differences amongst the models appears to be related to the amplitude of the trough. The UKMET appears to have the flattest trough in relation to the GFS and ECMWF, which allows a predominant south to north flow to not allow for such a quick recurvature.

Even though the ECMWF and UKMET solutions may be more closely related to the strength of the system, I am not completely confident that that is 100% the case, so I am not going to shift my forecast from yesterday, and I still expect a landfall along the coast of Mississippi on Saturday evening, likely closer to the Alabama border than the Louisiana border. There is margin for error on both sides, however, and areas from Houma, Louisiana to Apalachicola, Florida should monitor the progress of this system carefully.

I don't see anything stronger than 50 kt right now.

Probability of development in 48 hours: 90%

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

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8. WunderAlertBot (Admin)
8:27 AM GMT on October 04, 2013
KoritheMan has created a new entry.
7. wxchaser97
10:58 AM GMT on October 03, 2013
Thanks Kori! Maybe if you hadn't posted it at 3:43am I would've read it earlier... :P
Member Since: December 31, 1969 Posts: Comments:
6. traumaboyy
9:38 AM GMT on October 03, 2013
Good one Kori!!
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5. Bergwind
8:49 AM GMT on October 03, 2013
Hi KTM, All, I'm a newb here... but (unfortunately) not to Hurricanes. From New Orleans, Worked in network news covering storms for too long. Suffice... I've seen a few, and seen more than enough hysterical television coverage.

KTM, I think you have made a well considered analysis of what we're looking at so far with this one. I am concerned with it's size and am wondering what the projected size of the low pressure area might eventually be.
I'll be following your blog(S) Thanks. ';-)

Member Since: December 31, 1969 Posts: Comments:
4. mobilebayrat
7:55 AM GMT on October 03, 2013
Well, it made my stomach stop hurting enough that I think I can go catch a couple hours of sleep now, and we may be able to pull off the trip to the cross country meet!
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3. PensacolaDoug
7:55 AM GMT on October 03, 2013
Good analysis Kori. Now back to bed for me. Prolly have Karen by sunup.
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2. KoritheMan
7:51 AM GMT on October 03, 2013
Quoting 1. mobilebayrat:
Thank you! This is the most informative post I have read this evening. Don't care for where it looks like it is going, but I do like your ideas on the strength. I'll take that! :)


I just tell it like it is. All I can do, after all. :)
Member Since: December 31, 1969 Posts: Comments:
1. mobilebayrat
7:47 AM GMT on October 03, 2013
Thank you! This is the most informative post I have read this evening. Don't care for where it looks like it is going, but I do like your ideas on the strength. I'll take that! :)
Member Since: December 31, 1969 Posts: Comments:

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