500 MB PATTERN         OF  EAST COAST  HURRICANES

 

  There were a lot of various forecasts and discussion regarding the track in movement of hurricane Ophelia over the past several days. However back on September 9 -10 I need be forecasts and commitment that Ophelia would not be a significant threat to any portion of the East Coast... including far Eastern North Carolina and the Cape Code area of New England.

At the time I was the only one forecasting such a track... and several of my competitors including some of the more popular lines from the Keystone State where monitoring about potential for a significant I-95 Mid Atlantic and New England hurricane. This sort of unfounded mindless speculation and poor forecasting continue for several more days.

The problems with East Coast hurricanes is rather similar to the problems that forecasters faced with East Coast snowstorms. The simple appearance of a low pressure area on a weather model does not ensure it anyway that a snowstorm is likely to develop. Likewise... with regard to East Coast hurricanes... even when a fairly reliable global models such as the ECMWF is a showing a classic eastern NC NJ eastern New England track... one also has to take into account the overall pattern.

You would think that various hurricane models and even the global models would be able to handle the complicating interactions between tropical cyclones and the latitude whether features with some skill. However as Ophelia clearly shows that is not the case.

I cannot emphasize this point enough... it seems that no matter how many times I repeat it ... as long as the GFDL...ECMWF... or some other model shows a hurricane passing across the coastal areas of the East Coast... it is automatically assumed to be a valid solution regardless of what the upper pattern showing.

Such a idiotic assessment can only lead to disastrous forecasting... and those forecasters that went for a Eastern North Carolina hurricane and /or a East Coast hurricanes suffered the consequences of a busted forecast.

     

 

     This link has a complete listing of some very important rules for East Coast hurricane forecasting and instead of trying to monger up a scenario to trick people into extending or buying subscriptions to an overpriced weather service... some forecasters outa to spend more time taking a look at these rules.

http://www.wxrisk.com/hurricane/FrcstTechnq/forecastrules.html

The first rule that you have to keep in mind is that all things being equal.... a tropical cyclone will stay  along the immediate coast or  JUST off the coastal shorelines. There must be some mechanism to force the hurricane inland.

The second rule is that tropical cyclones ONLY come up the East Coast...be it inland... ride along the immediate  coast.... or just offshore... if and only if certain specific 500 mb / synoptic conditions exist. These conditions are for more important than ANY predicted track or intensity from any hurricane model.

 

  Let's take a look at some of these famous East Coast hurricanes and then we can compare them to the situation with Ophelia. This first case has to do with hurricane BELLE which occurred in AUG 8-10 1976. As you can see there was a upper low pressure area located over the Great Lakes which extended into the Midwest. The Upper winds along the East Coast were generally from a SW to NNE direction... which is not really ideal because such a direction does support a bend to the RIGHT as the TC moves up the East Coast. In addition with hurricane Belle there was no strong ridge of HIGH pressure in the West Atlantic Ocean.

belle.gif (66046 bytes)    

 

 

These next three maps have to do with hurricane Gloria from 1985 which was viewed as a major threat to the East Coast when she reached 919 MB at one point in the sw Atlantic Ocean. The first map shows he strong ridge of high pressure in the West in the western Atlantic Ocean BUT there is no 500 Low over the Great Lakes and certainly no trough over the Midwest.... in fact the cloth is a way out of position located over the Rockies Low pressure. Map 2-- 24 Sept 1985 - shows at the development of a large 500 MB Low over south-central Canada but again in this is NOT an ideal position because the trough is so   broad that the flow coming into the  East coast from the Midwest was  NOT due S to N... but again SW to NE... Much like BELLE in 1976.  Map 3 -- 25 Sept 1985- shows the 500 low actually moving to the northeast... towards a southwestern Hudson's Bay . Again this sets up a terrible position for a East Coast hurricane because the trough is still well west of the Mississippi River and the flow ahead in the trough coming into the East Coast is still at a Southwest which is going to cause Gloria to bend to the right... which is exactly what happened.

    gloria1.gif (41375 bytes) gloria2.gif (46761 bytes)gloria3.gif (91437 bytes)  

 

  These next to maps have to do with hurricane Floyd in September of 1999. Again much like Gloria Floyd was potentially major threat to the East Coast of the US... this time we have a 500 low area in a bit more favorable position over southwest Ontario... and the trough is right along the Mississippi River. There is a ridge of high pressure extending into West Atlantic into Florida... as Floyd approaches. However Map 2-- 12z SEPT 10-- sees the 500 MB low dropping the South into northern Minnesota... any trough extending all only down into Oklahoma and Arkansas. But what happens here is that the trough is pulled back to the West.... as the 500 Low moves west ...from the Ohio valley to the WEST of the Mississippi river. Again this produces too much of a Southwest wind flow which results in Floyd bending a little bit to the right.

 

    floyd.gif (43763 bytes)floyda.gif (67897 bytes)  

   Finally let's take a look at hurricane ISABEL in 2003 to study WHY it was so different. With Isabel we had a very strong ridge of high pressure in the West Atlantic Ocean.... but the trough was back across the Rockies 13 SEPT. in this case it turned out that the very strong ridge of high pressure in the West Atlantic Ocean prove to be crucial important with regard to a forcing mechanism to push Isabel in land.   isabel.gif (44091 bytes)   BY 15 Sept ... a Low at 500 MB coming out of the Lower Rockies ... and passing over Illinois... is an TEXT book set up . The 500 Low over ILL combine with the Ridge of High pressure in the Northwest Atlantic and New England area.... means a due S to N wind flow.

    isabela.gif (67680 bytes)           As you can see from these last two maps none of these conditions were even remotely present in any form whatsoever as Hurricane Ophelia meandered off the GA SC coast line .   

ecmwf_500_vort_h00.gif (128546 bytes)  ecmwf_500_vort_h72.gif (85693 bytes)