Craig's Inside Weather Scoop

A fairly decent cold front has moved through south Florida and cool air continues to filter into the area on Thursday.  The computer model temperature forecast (above) shows most areas of south Florida will drop into the mid to upper 50s with only coastal areas staying around 60 degrees.  The dry and pleasant weather will last through the weekend with more sunshine beginning Friday.

Update 5:45 AM , Tuesday 

From the National Hurricane Center

DATA FROM NOAA DOPPLER RADAR AND SURFACE OBSERVATIONS INDICATE THAT
THE CENTER OF TROPICAL STORM IDA MADE ITS FIRST LANDFALL AROUND 540
AM CST...1140 UTC...ON DAUPHIN ISLAND ALABAMA...WITH MAXIMUM
SUSTAINED WINDS OF 45 MPH...75 KM/HR.

----------------------------------------------------------
Ida, the late season, lopsided tropical storm is making landfall on the northern Gulf coast Monday night.  The main impact has been heavy rain and gusty winds. The moisture feed into Ida will be dragged over us on Tuesday night and Wednesday with a better chance for thunderstorms.

Monday morning visible satellite image of Ida.  Click image for Flash animation

After being the first November hurricane to form in the Caribbean in an El Nino year since hurricane Martha in 1969, Ida is being torn apart by increasingly hostile upper level wind shear.  The overall appearance of Ida in both the visible and microwave satellite images is that of a spiral more than a doughnut (strong storms surrounding eye in a circular pattern).


Monday morning satellite microwave (similar to weather radar) overpass showing thunderstorm pattern of Ida.

The shearing process, while causing Ida to weaken, is also creating a more lopsided storm with most of the wind and bad weather now stretching out well ahead of it.  The Monday morning shear analysis below shows even higher wind shear values immediately in front of where Ida is heading.


Monday morning Univ of Wisc upper wind shear analysis.  Note Ida near 30 knot wind shear contour with 50 knot wind shear contour over Florida Panhandle.

The effect of this much wind shear will be to rip Ida's thunderstorms away from its low level center.  While this is part of the weakening process, the strong surface wind field is still going to impact the northern Gulf coast through Tuesday.  Because of the approaching upper level trough, Ida's moisture and low pressure area are forecast to become part of a much larger low pressure storm system forming off the southeast US coast.  Some computer models show this with the early afternoon forecast and the Thursday forecast below.


GFS model forecast for Monday early afternoon.  Shaded colors indicate rainfall accumulations.  Note Ida's low pressure area in Gulf of Mexico on lower left side of image.



GFS model forecast for Thursday morning.  Shaded colors indicate rainfall accumulations.  Note low pressure area off southeast US (on right side of image).

For South Florida, the impacts should be gusty winds slowly decreasing into Wednesday with some thunderstorms possible Wednesday and Wednesday night.

UPDATE:  9:15 AM Sunday

Ida has intensified to a hurricane as forecast and is moving more northwest, also as forecast.  Any significant direct impact from Ida to South Florida is extremely unlikely.  Some secondary effects such as heavy rainfall and gusty winds is possible during the middle of the week as moisture from Ida moves our way.  One immediate effect for Sunday and Monday is very strong winds. Below is the Sunday morning surface pressure analysis.  You can see the high pressure area along the east coast and the low pressure associated with Ida near the Yucatan of Mexico.  The tightly packed black lines across Florida indicate the pressure difference or gradient is very strong, thus the strong winds.
 


Here are the latest wind speeds for south Florida below.


---------------------------------------------------------------------------------------

UPDATE: 8:40 PM Saturday

No changes as of Saturday evening with respect to the forecast for Ida's intensity or forecast track.  Ida is just below hurricane strength.  Hurricane hunters and hurricane research aircraft will be monitoring the cyclone closely over the next several days now so we will have a good idea if it's on track and intensity or doing something unexpected. 

Besides being close to the intensity forecast, Ida is also turning a little bit left or west of due north so now it's moving closer to it's forecast direction of north-northwest.  This is important because a north motion would have brought it potentially closer to the Keys but north-northwest will take it into the southeast and central Gulf of Mexico.  Stay tuned.

-----------------------------------------------------------------------------------------
Saturday, November 7, 10:40 AM

Ida was able to make it across the land of Nicaragua and Honduras for a couple of days with minimal impact to the overall circulation.  Now that it's over the very warm waters of the western Caribbean, and still in relatively low shear, Ida is strengthening.  The latest satellite images show a tropical storm that continues to become better organized.


Click on the above image for the latest Flash player satellite animation.

Most of the intensity forecast models show a continued strengthening bringing Ida to a strong tropical storm or category one hurricane by Sunday.



Saturday morning model intensity forecast.  Time line is from left to right, 24 is Sunday morning, 48 is Monday morning, etc.  Intensity is the up/down scale.  Note models show intensification, then leveling off, then decreasing intensity by Tuesday.  Intensity forecasting is one of the most difficult aspects of hurricane forecasting.

After that a combination of increasing upper shear and a decrease in the ocean temperatures should result in leveling off of the intensification or even a slow decrease in intensity.  The one unknown is the effect an upper level trough will have on Ida.  Many times the strong upper winds shear a tropical system apart or cause it to transition into some other type of low.  At the same time the upper level energy from that trough can intensify a tropical system as it transitions from what we think of as a "purely" tropical cyclone to a non-tropical or extra-tropical low.  These non-tropical lows are what we typically see over the US bringing heavy rains, snows, and winds.  They get some of their strength from the colder air aloft and the strong wind fields.  This cold air aloft and strong wind field rarely exists at the same time with a tropical system.  But if you bring a tropical system into the cold upper air and strong winds, sometimes they can intensify.  That's something we will watch for with Ida early next week.  The most likely scenario is Ida will be overwhelmed by the upper trough and cold front and be pushed (crushed) eastward into the eastern Gulf of Mexico.


All of that being said, I still believe the main impact to South Florida will be from the tropical moisture and that won't occur until midweek when we may see thunderstorms and heavy rains with gusty winds.  Here are the latest model forecast tracks and as long as Ida doesn't head up the right side of the tracks (something Irene did in 1999) we should be in pretty good shape in South Florida.  We will watch for that "rightward" bias of the storm very closely.

Besides the future track cone created by the National Hurricane Center, we also have a product called "Wind Force Probability".  It's basically the overall probability a given location will see tropical storm force winds in the next five days.  Here are the latest probabilities for Ida.  This graphic is updated every six hours with each new forecast advisory from the hurricane center.  Check back often.

If, and that's a big if, Ida survives the transit across Nicaragua and Honduras, then the much weakened circulation will emerge over some deep warm water in the northwest Caribbean.  It will nearly be starting from square one as it will have to develop thunderstorms near and over the center again, lower the pressure, and tighten up the wind field.  These regeneration processes can happen quickly with large, well organized hurricanes like Wilma that passed across south Florida and then restrengthened back to category three over the Atlantic.   But in this case, Ida was just barely a hurricane as it made landfall Thursday morning and had a much smaller wind field.  So one would think it's going to take longer for restrengthening to occur if at all.

The graphic below is the most recent analysis of Ocean Heat Content, a measure of not only the warmth of the water, but the depth of the warm water too.  We look at this because shallow warm water on the surface with cold water underneath contains less heat energy for tropical storms and hurricanes, especially slow moving ones.  While I labeled the graphics warm and cooler water, it would probably be more correct to say "greater heat content" and "less heat content".

So the ocean energy for a restrengthening tropical system is there.  But some other ingredients are not going to be there soon, namely low wind shear.


Early November Ocean Heat Content.

Below is the Thursday afternoon middle atmospheric shear analysis.  There is a deep upper trough over Mexico and moderate westerly shear downstream over the Gulf of Mexico.  This should have a pretty good limiting effect on the intensification of Ida as it approaches the Gulf.  And what may happen is the Ida circulation and it's tropical moisture just gets absorbed into the larger low pressure area forecast to develop in the Gulf.



One thing looks fairly certain, this is going to bring a lot of rain and storms to a large portion of the Gulf and Southeast US next week and some storminess is likely for Florida too.  Stay tuned.

The National Weather Service in Miami released their South Florida winter forecast on Thursday and based on the El Niño pattern we are in, there are no big surprises.

El Niño is a warming of the waters in the central and eastern Pacific Ocean.  The animations to the left show the actual temperatures and the anomaly (difference from normal).  You can see the warm anomalies are persisting and in some spots even increasing. 

In an El Niño summer the upper level winds are a little stronger and more disruptive to hurricanes and we see less overall hurricane activity like this year.  In an El Niño winter the sub-tropical or southern branch of the jet stream is a little stronger and will combine with the polar or northern branch of the jet stream to create a more active weather pattern.  Specifically for south Florida we see frequent periods of windy and rainy days with some severe weather outbreaks (thunderstorms with tornadoes).  Because of the extra clouds and rain, temperatures are usually cooler than normal. 

So to sum it up, expect clouds, wind, and showers several days a week with fewer sunny periods.   Highs will often stay in the 60s and low 70s with lows in the 50s.  Occasionally a severe weather outbreak is possible, especially from late January through March.

Our little bit of fall weather was nice...while it lasted.  Unfortunately for those of us who like a little dry season with our long tropical summers, the heat and humidity are back to stay for the week.  The computer models through at least Wednesday show summer time humidity levels over all of Florida with the dry, autumn air just to our north.


Computer model forecast of surface moisture for Wednesday.  Red indicates higher humidity values.

The pattern looks a little like the one we saw a couple of weeks ago but not quite as hot.  The longer nights and lower sun angle also keep us from highs in the low to mid 90s this time of year but much of the week we will see highs around 90.

Update, Saturday 8:00 AM

The weak low pressure area heading toward south Florida from the Bahamas remains disorganized and has little chance of turning into a tropical depression or tropical storm.  That being said, it does look like it will keep our rain chances high both Saturday and Sunday.



--------------------------------------------------------------------------------------------------------------------
Friday afternoon blog entry
The tropical disturbance in the western Caribbean has fizzled out for the time being but the remnants of a cold front and low pressure trough over the Bahamas is trying to come to life.  Because of how close it is to south Florida it's something we'll need to watch.  Its proximity to us means if it develops, we would have very little time to get ready if it came this way.  Fortunately also, its proximity to us means it wouldn't have a lot of time to develop if it came this way.  So we will have to watch for the possibility of  tropical development with the most likely results being some heavy rain and gusty breeze....if it comes this way!  The models are suggesting it will be close as it moves northwest but then likely turns north because of the next dip in the jet stream.  Hurricane hunters may investigate this disturbance tomorrow.

Stay tuned.

What a great weekend this past weekend was.  We managed a record high on Saturday at MIA of 92 and then a record minimum high on Sunday of just 71.  That's a 21 degree cold front, a pretty big deal by October south Florida standards.  And the low at Ft Lauderdale set records two days in the row immediately following the cold front at 58 and 56 for Sunday and Monday mornings.  Cool stuff, literally.

But this time of year we hang on the edge of getting into the winter season and getting out of the tropical season and sometimes things can get dicey.  And these days we're watching a tropical disturbance sitting in the western Caribbean.


During the summer these tropical disturbances almost always move west into Central America with the easterly trade winds.  But late in the summer and fall the dips in the jet stream or troughs reach way down into the Caribbean and can often lift a tropical system out to the north or northeast.  So this is the time of year we don't watch the Atlantic but do watch the Caribbean.

According to the National Hurricane Center climatology for October, Florida is fairly vulnerable to tropical systems that form in the western Caribbean.


NHC October climatology of hurricane formation and tracks.

A couple of hurricanes of note that formed in the western Caribbean and threatened or impacted south Florida are Michelle in 2001.



And of course Wilma in 2005.



So this disturbance in the western Caribbean will be something we watch in the coming days, and hope it doesn't pay a visit to south Florida!


Computer model forecast tracks for western Caribbean distrubance, AL94