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posted on 24 September 2017

Out to Sea but is the Track Forecast Reliable? - 24Sep2017

Written by Sig Silber

This Article has been updated. You can access the update at: "Out to Sea but is the Track Forecast Reliable? - 25Sep2017"

5:30 PM EDT Sept 24, 2017: LATEST FROM NHC: "...TROPICAL STORM AND STORM SURGE WATCHES ISSUED FOR A PORTION OF THE COAST OF NORTH CAROLINA... " "The latest runs of the dynamical models are fairly similar to the previous ones...The NHC track...lies west of the various consensus aids out of respect for the ECMWF and its ensemble mean."

Special Landing Graphic for Possible Hurricane Maria - Will Maria Stay on track?

 It increasingly looks like Maria will stay on track and just graze the Cape Hatteras area and inland from there to a fairly limited extent. We will continue to update this report. 

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This remains an active period in the tropics so we are starting with the overview of the situation in both the Pacific and the Atlantic even though right now only the Pacific presents major threats. Those potentially impacted by any of these storms should consult their local sources of information. The Public Advisories and other information that is available from the NOAA National Hurricane Center can be found here. Information from the Weather Prediction Center can be found here.

First the Atlantic

Eastern Tropical Pacific 

And now the Pacific

Eastern Tropical Pacific

We start our Report with Hurricane Maria. The"M" Designation means a very powerful storm: Category 3 or higher.  Notice that Maria no longer categorized as "M". 

Tropical Depression 15

Maria Wind Speed Probabilities

Experimental Wind Arrival Analysis

And the Discussion

Hurricane Maria Discussion Number 35 NWS National Hurricane Center Miami FL 500 PM EDT Sun Sep 24 2017

Recent reports from NOAA and Air Force Reserve Hurricane Hunter aircraft indicate that Maria's pressure has fallen a few millibars since this morning, but there has been little overall change in intensity.  A blend of the flight-level and Stepped Frequency Radiometer Microwave Radiometer data yields an initial wind speed of around 90 kt.  Maria will be traversing warm water and remain in a low shear environment during the next day or so, and some fluctuations in intensity are possible through Monday. After that time, Maria is forecast to move over cooler waters left over from Hurricane Jose.  This is likely to result in gradual weakening, however Maria is forecast to maintain hurricane status through the entire forecast period.

Maria is moving just west of due north or 350/8 kt. The hurricane is currently being steered north-northwestward to northward between a cut-off low over the southeastern U.S. and a subtropical ridge over the southwestern Atlantic. The forward motion of the hurricane should slow down over the next couple of days as a ridge builds to the north of the system over the northeastern United States.  After 72 h, Maria should turn east-northeastward and begin to recurve as the deep-layer flow turns southwestward ahead of large mid-latitude trough that is forecast to move over the Great Lakes region by the end of the week.  The latest runs of the dynamical models are fairly similar to the previous ones, with the ECMWF along the western side of the guidance and the GFS near the eastern edge.  The NHC track is between these solutions, and lies west of the various consensus aids out of respect for the ECMWF and its ensemble mean.

Since Maria is a large hurricane, the associated tropical-storm-force winds could reach a portion of the North Carolina in about 48 hours.  As a result, a Tropical Storm Watch has been issued for a portion of the coast of North Carolina.


1. Maria is forecast to continue moving northward, paralleling the U.S. east coast, and it is likely that some direct impacts will occur along portions of the coast beginning Tuesday, and a Tropical Storm Watch has been issued for a portion of the coast of North Carolina.

2. Storm surge flooding especially along the sound side of the North Carolina Outer Banks is possible beginning Tuesday, and a Storm Surge Watch has been issued for a portion of the North Carolina Outer Banks.

3. Swells from Maria are increasing along the coast of the southeastern United States and are expected to reach the Mid- Atlantic coast today.  These swells will likely cause dangerous surf and rip currents at beaches in these areas through much of the week.  For more information, please monitor information from your local National Weather Service office at


INIT  24/2100Z 29.4N  73.0W   90 KT 105 MPH

12H  25/0600Z 30.3N  73.2W   90 KT 105 MPH

24H  25/1800Z 31.4N  73.4W   85 KT 100 MPH

36H  26/0600Z 32.5N  73.5W   80 KT  90 MPH

48H  26/1800Z 33.6N  73.6W   80 KT  90 MPH

72H  27/1800Z 35.0N  73.3W   75 KT  85 MPH

96H  28/1800Z 35.8N  71.0W   65 KT  75 MPH

120H  29/1800Z 37.5N  64.5W   65 KT  75 MPH

Vertical Wind Shear is one factor now starting to diminish Maria.

Effects of vertical wind shear

Learn more about wind shear here.

New Storm: Tropical Storm Pilar


Tropical Storm Pilar Discussion Number  5 NWS National Hurricane Center Miami FL 400 PM CDT Sun Sep 24 2017

Pilar continues this afternoon to be a problematic system. Fortunately, a 1426Z GPM 36 GHz image suggested that the system's center was very close to Cabo Corrientes at that time.  This allowed for a somewhat better estimate of the initial position and motion (350 degrees at 7 kt).  Pilar is being advected around a deep-layer ridge located over central Mexico.  Despite the initial continued movement at around 7 kt this afternoon, the guidance insists that Pilar should soon slow down.  The official forecast track is quite similar to the previous one, with a course along or just west of the coast of southwestern Mexico.  Fortunately, the model guidance came into better agreement with the track prediction, though some of the model's trackers could not explicitly follow the weak vortex beyond a day or so into the future.

Because of Pilar having some of its circulation over the high terrain of southwestern Mexico, some weakening has likely occurred. The initial intensity is reduced to 35 kt, based upon a blend of the TAFB and SAB Dvorak classifications.  While the SSTs are warm and the vertical shear is only moderate for the day or so, continued interaction with land is likely to prevent any re-intensification. After about 24 hours, the vertical shear should go way up, as Pilar is affected by strong southerlies associated with a vigorous mid- to upper-tropospheric trough over the southwestern United States.  The official intensity forecast is closest to a blend of the LGEM statistical scheme and the HWRF dynamical model, and is just slightly below the previous advisory.  An alternative scenario is for Pilar to dissipate substantially sooner because of the land interactions.


INIT  24/2100Z 20.8N 105.8W   35 KT  40 MPH

12H  25/0600Z 21.8N 106.0W   35 KT  40 MPH

24H  25/1800Z 22.5N 106.2W   30 KT  35 MPH

36H  26/0600Z 23.0N 106.5W   25 KT  30 MPH

48H  26/1800Z 23.5N 107.0W   20 KT  25 MPH...POST-TROP/REMNT LOW

72H  27/1800Z...DISSIPATED

General Weather Situation

We believe that it is easier to understand what is going on with individual storms if they are put into the context of the overall weather situation.

Three day

The graphic above is particularly useful as it shows the forecasted conditions that might determine the future of a storm beyond the predictions of where the storm might be on Day 3. This graphic is updated frequently. There is still a possibility that Maria and Lee will interact at least indirectly. The High forecast to be to the Northeast of Maria remains the key to Maria being able to turn right or be forced to hug the coast.

Some of the graphics below show the two storms of most interest.

Day 1 Forecast Map

Day 2 Forecast

This is a Day 2 Forecast.  Notice Jose has been Downgraded but is still hanging around.

Additional Graphics

More explanation on Atmospheric Rivers can be found by clicking here or if you want more theoretical information by clicking here.


Note that this graphic has not been updating since September 20. We could remove it but I hope it will start to work soon so we are leaving it in for now but the dates of update are clearly shown at the top of the graphic.

Atmospheric Rivers

This is a national animation of weather fronts and precipitation forecasts with four 6-hour projections of the conditions that will apply covering the next 24 hours and a second day of two 12-hour projections the second of which is the forecast for 48 hours out and to the extent it applies for 12 hours, this animation is intended to provide coverage out to 60 hours. This graphic is very relevant as one can see both storms of most interest in this graphic. .

current highs and lows

The explanation for the coding used in these maps, i.e. the full legend, can be found here although it includes some symbols that are no longer shown in the graphic because they are implemented by color coding.

Precipitation Forecast

You can see the forecast for seven days of cumulative precipitation. It is important to keep in mind that these are forecasts going forward. Precipitation that has already occurred does not show up in these forecasts but will show up in the 30 day maps we show in our weekly Weather and Climate Report. That did not show up in our September 11 Report but did show up in the September 18 Report that was issued Monday evening click here to read. You can see the current QPF for Maria. Separate from Maria ,we see a concerning situation for Southwest Texas. It is also tropical moisture.

 Water Vapor Imagery

The water vapor imagery is a good guide to where precipitation is occurring. Jose is gone. One sees Maria off shore. The outer bands are starting to impact the Carolinas. One can see Pilar off the west coast of Mexico.

Click here for a list of Sig Silber's Weather Posts

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