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Atlantic Tropical Action 2013 - Part 2

HurricaneJosh

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WxFreak11

WxFreak11

Posted
Posted

What is the deal with this 98L? Wish it was something cause a lot of the paths would be putting it in good position.

 

storm_98.gif

 

Quite a few of the models do put 98L in a good position but I think condtions aren't that favorable right now. Nobody is talking about this storm because again..we've all been burned one too many times this season. This season is just one big cluster! :thumbsdown:

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TropicalAnalystwx13

TropicalAnalystwx13

Posted
Posted

Maybe someone here knows since I've asked around and nobody else seems to...

 

All I keep hearing is that the LGEM and SHIPS should be used only after a tropical cyclone develops because they're run as if one already exists...but what are the specifics behind that? Are they initialized with a false circulation or something along those lines?

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Ed Lizard

Ed Lizard

Posted
Posted

Maybe someone here knows since I've asked around and nobody else seems to...

 

All I keep hearing is that the LGEM and SHIPS should be used only after a tropical cyclone develops because they're run as if one already exists...but what are the specifics behind that? Are they initialized with a false circulation or something along those lines?

 

Simpler than that, really.  From the NHC page... 

I know the difference between statistical, statistical-dynamic and dynamic models, but not so well I can explain them really well.  But SHIPS is fairly simple compared to the dynamic models.  SHIPS does not model the actual storm, whether it is a real storm or depression, its predictions are based on several factors that favor or not favor the storm reaching its MPI, it doesn't model an actual storm.

Statistical Hurricane Intensity Prediction Scheme (SHIPS)

The SHIPS model is a statistical-dynamical intensity model based on statistical relationships between storm behavior and environmental conditions estimated from dynamical model forecasts as well as on climatology and persistence predictors. Due to the use of the dynamical predictors, the average intensity errors from SHIPS are typically 10%-15% less than those from SHIFOR5. SHIPS has historically outperformed most of the dynamical models, including the GFDL, and SHIPS has traditionally been one of the most skillful sources of intensity guidance for NHC.

SHIPS is based on standard multiple regression techniques. The predictors for SHIPS include climatology and persistence, atmospheric environmental parameters (e.g., vertical wind shear, stability, etc.), and oceanic input such as sea surface temperature (SST) and upper-oceanic heat content. Many of the predictors are obtained from the GFS and are averaged over the entire forecast period. The developmental data from which the regression equations are derived include open ocean TCs from 1982 through the present. Each year the regression equations are re-derived based upon the inclusion of the previous year.s data. Therefore, the weighting of the predictors can change from year to year. The predictors currently found to be most statistically significant are: the difference between the current intensity and the estimated maximum potential intensity (MPI), vertical wind shear, persistence, and the upper-tropospheric temperature. SHIPS also includes predictors from satellite data such as the strength and symmetry of convection as measured from infrared satellite imagery and the heat content of the upper ocean determined from satellite altimetry observations.

DeMaria M., and J. Kaplan, 1994: Sea surface temperature and the maximum intensity of Atlantic tropical cyclones. J. Climate, 7, 1324.1334.

DeMaria, M., M. Mainelli, L.K. Shay, J.A. Knaff, and J. Kaplan, 2005: Further Improvements to the Statistical Hurricane Intensity Prediction Scheme (SHIPS). Wea. Forecasting, 20, 531.543.

 

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MJO812

MJO812

Posted
Posted

It looks like we will have a TD soon

 

http://www.nhc.noaa.gov/gtwo_atl.shtml

 

1. SHOWERS AND THUNDERSTORMS ARE GRADUALLY BECOMING BETTER ORGANIZED NEAR A LOW PRESSURE SYSTEM CENTERED ABOUT 325 MILES EAST-SOUTHEAST OF THE SOUTHERN CAPE VERDE ISLANDS. ENVIRONMENTAL CONDITIONS APPEAR CONDUCIVE FOR FURTHER DEVELOPMENT...AND A TROPICAL DEPRESSION COULD FORM DURING THE NEXT DAY OR SO WHILE THE DISTURBANCE MOVES WEST-NORTHWESTWARD AT ABOUT 10 MPH TOWARD THE CAPE VERDE ISLANDS. THIS SYSTEM HAS A HIGH CHANCE...70 PERCENT... OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS...AND A HIGH CHANCE...90 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 5 DAYS. INTERESTS IN THE CAPE VERDE ISLANDS SHOULD MONITOR THE PROGRESS OF THIS SYSTEM...AND TROPICAL STORM WATCHES OR WARNINGS COULD BE REQUIRED IF A DEPRESSION FORMS. REGARDLESS OF TROPICAL CYCLONE FORMATION...HEAVY RAINFALL AND GUSTY WINDS ARE POSSIBLE IN THE CAPE VERDE ISLANDS BY LATER TODAY.

 

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Ed Lizard

Ed Lizard

Posted
Posted

The GFS per NHC just relocates the vortex to best track, it doesn't create a fake (bogus) one.  Note also why 98L may not be in a hurry to develop.

 

 

 

The GFS makes a special accommodation for TCs in its initial fields by relocating the globally analyzed TC vortex in the first-guess field to the official NHC position. An assimilation of the available data is then performed to create the initial state. The globally analyzed vortex is, however, often an incomplete representation of the true TC structure. For this reason, the GFS is typically more suited to producing track and outer wind structure forecasts than to producing intensity forecasts.

 

 

http://www.nhc.noaa.gov/modelsummary.shtml

 

 

 

Beta and Advection Model (BAM)

 

The Beta and Advection Model (BAM) refers to a class of simple trajectory models that utilize vertically averaged horizontal winds from the GFS to compute TC trajectories. These trajectories include a correction term to account for the impact of the earth.s rotation. The BAM is based upon the concept of a simple relationship between storm intensity/depth and steering levels. Strong cyclones typically extend through the entire depth of the troposphere and are steered by deeper layer-average winds, while weaker cyclones are steered by shallower layer-average winds. The BAM is run in three versions corresponding to the different depths used in the trajectory calculation: BAM shallow (850-700 mb), BAM medium (850-400 mb), and BAM deep (850-200 mb), known as BAMS, BAMM and BAMD, respectively. The performance of the BAM is strongly dependent on the dynamical input from the GFS. A divergence of the three versions of the BAM indicates varying steering flow within the parent GFS model. Hence, spread among the three versions of the BAM also serves as a rough estimate of the vertical shear as well as the complexity and uncertainty in the track forecast.

 

 

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Derecho!

Derecho!

Posted
Posted

Maybe someone here knows since I've asked around and nobody else seems to...

 

All I keep hearing is that the LGEM and SHIPS should be used only after a tropical cyclone develops because they're run as if one already exists...but what are the specifics behind that? Are they initialized with a false circulation or something along those lines?

 

They are quite simple statistical models (that still are as or more more accurate than far more complex dynamic models like the GFDL and HWRF).  Actually, all intensity models used for INVESTS are pretty much garbage. The GFDL and HWRF do even worse for INVESTS.

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Ed Lizard

Ed Lizard

Posted
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They are quite simple statistical models (that still are as or more more accurate than far more complex dynamic models like the GFDL and HWRF).  Actually, all intensity models used for INVESTS are pretty much garbage. The GFDL and HWRF do even worse for INVESTS.

 

My observation with GFDL and invests, whether the GFDL can track a vortex over the entire run is a useful predictor as to whether the invest will develop.  Not perfect, but useful.

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TropicalAnalystwx13

TropicalAnalystwx13

Posted
Posted

The 12z GFS is the most bullish run so far regarding development in the Bay of Campeche in a few days. Genesis appears  to be related to the surface trough already positioned there with maybe some added energy from the northern portion of the tropical wave axis in the Gulf of Honduras.

EDIT: And thanks for the responses above guys.

 

t5ymDvh.png

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phil882

phil882

Posted
Posted

The 12z GFS is the most bullish run so far regarding development in the Bay of Campeche in a few days. Genesis appears  to be related to the surface trough already positioned there with maybe some added energy from the northern portion of the tropical wave axis in the Gulf of Honduras.

EDIT: And thanks for the responses above guys.

 

t5ymDvh.png

 

Don't expect much out of the GOM system, its a very gyre like configuration where multiple meosvorticies are fighting for dominance in a much larger scale cyclonic circulation. 

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phil882

phil882

Posted
Posted

And a lot of it is over either Central America or the Eastern Pacific per the GFS.

 

Correct... which is typical for CA gyres. There are instances that CA gyres spin up into formidable TCs, but thats rare, and happens most often when the gyre circulation becomes established far enough away from CA and the vorticity can become focused in one particular region (ex. Roxanne 1995, Wilma 2005, Sandy 2012)

 

A good analog for the best case scenario (in terms of TC intensity) for this possible gyre to TC evolution is likely what happened with Stan (2005). The storm was rapidly intensifying in the BOC before it made landfall in Mexico.

 

http://www.atmos.albany.edu/student/ppapin/lb13_img/special/20130908/gyre_05.html

 

Note that the gyre circulation axis (blue TC symbol) is south of TC Stan though most of its lifespan. Since Stan is embedded in a larger circulation, the general rule of thumb is that it should rotate cyclonically around this larger circulation, which is why you see Stan dive southward (which was unexpected at the time) 

 

The two graphs at the bottom are used to diagnose if you have a CA gyre. The two necessary criteria in this case are whether or not the circulation is closed (arc averaged tangential wind must exceed 1 ms^-1) and the maximum azimuthally averaged tangential wind must exceed 5 ms^-1 while also occurring greater than 500 km from the gyre center. This filters out TC like disturbances where the radius of maximum wind would likely be within 500 km.

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phil882

phil882

Posted
Posted

91L failing at a recurve and then menacing the Canadian Maritimes beyond 10 day ala Euro would be interesting.  Not for the purists, obviously...

 

91L gets ripped apart by shear long before it has a chance to threaten any land mass in the long range. Part of reason why 91L recurves so early is due to the anomalosly deep and upper-level trough. 

 

21n2mfp.gif

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Ed Lizard

Ed Lizard

Posted
Posted

91L gets ripped apart by shear long before it has a chance to threaten any land mass in the long range. Part of reason why 91L recurves so early is due to the anomalosly deep and upper-level trough. 

 

21n2mfp.gif

 

The Euro weakens it dramatically, but keeps a closed low the entire 10 days for 09L.  Starts intensifying again at the end of the run, I assume as it begins transition to a post-tropical low. 

 

Weenie speculation, the low off New England is obviously frontal per Euro 850 mb temps, but pretty intense, and over 20 to 25C water temps, and looking like the Euro wants to cut it off and drift it Southward in the mid-levels. 

 

So far, every weenie speculation I have had about Euro Day 9 or 10 cutoff lows have resulted in fail this season.

post-138-0-96025200-1378670025_thumb.gif

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Ed Lizard

Ed Lizard

Posted
Posted

How many Category Five hurricanes have hit Mexico, from either the Atlantic or Pacific Ocean?

 

At least one.  I know of this one only because Josh mentioned it on the Pacific thread...

 

 

http://en.wikipedia.org/wiki/1959_Mexico_Hurricane

 

 

Edit to add- Internet fu says 1 on the Atlantic side (Janet), or two total, by my amateur account

 

Edit 2  Wiki, the source of all knowledge suggests Tampico 1933 could have still been a Cat 5 when it hit the Yucatan, but the tree fell in the forest, and officially is a Cat 4.    Interesting, Josh territory, if US landfalls may have had a high bias in the pre-satellite/recon era, perhaps non-US landfalls with limited observations could have a low bias.

 

http://en.wikipedia.org/wiki/List_of_Category_5_Atlantic_hurricanes

 

I also wonder if there is a positive land bias, almost all Atlantic Cat 5s have made landfall at some strength, per the article.

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Amped

Amped

Posted
Posted

GFDL shows 992mb but only 46kts at 72 hrs.

 

This storm does have pretty good water temps a moist environment and low shear for the next 4 days. On the other hand models don't really take it below 990mb and it has a broad circulation, so it may require a lower pressure to become a hurricane.  I give it about a 30% chance of becoming a hurricane withing 72 hrs and a 60% chance of becoming one at some point. If it were a normal year, I'd say CAT 2 before 12z on the 11th.

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