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posted on 23 September 2017

Out to Sea but is the Track Forecast Reliable? - 23Sep2017

Written by Sig Silber

This Article has been Updated. You can access the updated article by clicking on: Out to Sea but is the Track Forecast Reliable? - 24Sep2017

Updated 6:20 PM EDT Sept 23, 2017:  LATEST FROM NHC: "...MARIA CONTINUES NORTH-NORTHWESTWARD... ...INTERESTS ALONG THE CAROLINA AND MID-ATLANTIC COASTS SHOULD MONITOR THE PROGRESS OF MARIA..." "Maria's forecast track has shifted closer to the U.S. east coast, and it is becoming increasingly likely that some direct impacts will occur along portions of the coast next week."

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

The Maria Track does not provide comfort that we will not hear from Maria again re CONUS Northeast and Canada or even Cape Hatteras. Stay tuned on this one as it will be days before we really know what to expect. 

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Damage Reports from the recent impacts of Hurricane Maria start to trickle in. Here is one. And here is an impact assessment and analysis and an update from the same source.    This report is focused on Puerto Rico. Our coverage on impacts will expand as more information becomes available.

Preliminary Puerto Rico Rainfall Totals

This report is particularly concerning. But it appears to have been a precautionary evacuation due to critical water levels having been reached rather than a dam failure but we can not confirm this. The Author of this GEI Article is responsible for seven flood control dams and is aware of typical Emergency Actions Plans and the best time to evacuate is prior to the dam actually failing.

This is 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 

More Detail


Map Source: Kmusser

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.  

Tropical Depression 15

There are two key issues. First of all is the question of how far west the track will be. Then the second and probably most important issue is when the track turns out to sea. The current forecast is that this will happen sometime after Wednesday morning. If it is delayed by one day that is a problem.

Maria Wind Speed Probabilities

Experimental Wind Arrival Analysis

And the Discussion

Hurricane Maria Discussion Number 31 NWS National Hurricane Center Miami FL 500 PM EDT Sat Sep 23 2017

Maria's eye became cloud filled again today, although convective cloud tops have been cooling within the eyewall during the past couple of hours.  A NOAA Hurricane Hunter plane conducting a research mission has not yet sampled the entire circulation, but they did report that the central pressure had fallen by a couple of millibars.  In addition, a Coyote unmanned aerial vehicle launched by the plane has been measuring winds of 120-125 kt at altitudes of 1200-1300 ft, which supports maximum surface winds of 100 kt.

The initial motion remains north-northwestward, or 345/8 kt, but Maria is expected to turn northward by this evening or overnight while moving between a mid-level high near Bermuda and a cut-off low over the northeastern Gulf coast.  A blocking ridge sliding eastward over the northeastern U.S. should cause Maria to slow down to a forward motion of 5 kt or less beginning in about 36 hours, lasting through the end of the forecast period.  The track models appear to have stabilized for the moment, with this being the first cycle in about a day where they have not shown a significant westward shift. Therefore, the updated NHC track forecast is relatively unchanged from the previous forecast during the first 3 days.  The day 4 point was shifted a little closer to the North Carolina coast to be closer to the consensus aids and the Florida State Superensemble, and all the models indicate that a northeastward motion away from the coast should begin by day 5.

Vertical shear will remain relatively low over Maria for the next several days, and the hurricane will be moving over warm waters at least for the next 3 days.  However, the depth of the thermocline does become more shallow, with oceanic heat content values steadily decreasing over the next 36 hours.  With Maria expected to slow down, upwelling of colder water becomes a greater factor, and that could modulate the hurricane's intensity during the next several days.  Maria also could still move over Jose's cold wake in 4-5 days, which would likely cause additional weakening.  The NHC intensity forecast remains just above the intensity consensus, however it should be noted that the normally skillful HCCA model is toward the lower end of the guidance suite.  It therefore wouldn't be surprising if Maria weakened more than shown in the official forecast.


1. Maria's forecast track has shifted closer to the U.S. east coast, and it is becoming increasingly likely that some direct impacts will occur along portions of the coast next week.  Interests along the coast of the Carolinas and the Mid-Atlantic should monitor the progress of Maria, as tropical storm or hurricane watches may be needed for part of this area on Sunday.

2. Swells from Maria are increasing along the coast of the southeastern United States and are expected to reach the Mid-Atlantic coast tonight and on Sunday.  These swells will likely cause dangerous surf and rip currents at the beach through much of next week.  For more information, please monitor information from your local National Weather Service office at


INIT  23/2100Z 26.3N  72.5W  100 KT 115 MPH

12H  24/0600Z 27.6N  72.8W  100 KT 115 MPH

24H  24/1800Z 29.1N  73.1W  100 KT 115 MPH

36H  25/0600Z 30.1N  73.3W   95 KT 110 MPH

48H  25/1800Z 31.1N  73.3W   90 KT 105 MPH

72H  26/1800Z 32.9N  73.3W   80 KT  90 MPH

96H  27/1800Z 34.5N  73.5W   70 KT  80 MPH

120H  28/1800Z 35.0N  72.0W   65 KT  75 MPH

Vertical Wind Shear is one factor now starting to diminish Maria. It may be a factor off and on depending on where Maria is.


Effects of vertical wind shear

Learn more about wind shear here.

New Storm: Tropical Depression Eighteen-E



Tropical Depression Eighteen-E Discussion Number  1 NWS National Hurricane Center Miami FL 400 PM CDT Sat Sep 23 2017

ASCAT-A/-B scatterometer data from around 16-17Z indicated that the low pressure system located just offshore of the southwestern coast of Mexico that the NHC has been tracking the past several days has become much better defined, and it also possessed surface winds of 30-33 kt. As a result, the system has been upgraded to a tropical depression, the eighteenth of the eastern Pacific hurricane season.

The initial motion estimate is 335/04, based primarily on microwave satellite fixes. The latest NHC model guidance is in fairly good agreement on the cyclone moving slowly in a general north-northwestward direction around the western periphery of a deep-layer ridge for the next 5 days. Some of the models like the GFS, Canadian, and HCCA take the system just inland near Cabo Corrientes in about 24 hours, whereas the remainder of the guidance, especially the UKMET and ECMWF, keep the cyclone just offshore of the southwestern coast of Mexico. The forecast motion for the next few days is expected to be 5 kt or less, an indication that steering currents will be weak. Since there is no strong forcing that would want to drive the depression inland over the mountainous terrain of southwestern Mexico, the official forecast calls for the center of the cyclone to remain just offshore of the coast throughout the forecast period, similar to the ECMWF and UKMET solutions.

Given the well-defined circulation noted in the aforementioned scatterometer data, along with vertical wind shear decreasing to less than 10 kt by 24 hours, steady strengthening is forecast for the next 24-36 hours. Afterwards, southeasterly to southerly shear is expected to gradually increase to 25 kt by 72 hours and more than 30 kt in the 96-120 hour period, which should induce steady to possible rapid weakening. The NHC intensity forecast is above most of the guidance through 48 hours, and then is a little lower than the guidance after that.

Due to the depression being forecast to become a tropical storm by tonight, along with its proximity to the coast of Mexico, a tropical storm warning has been issued from Manzanillo northward to El Roblito, including the Islas Marias. Heavy rainfall causing flash floods and mudslides will also be possible within the warning area and extending well inland.


INIT  23/2100Z 18.4N 105.3W   30 KT  35 MPH

12H  24/0600Z 18.8N 105.5W   40 KT  45 MPH

24H  24/1800Z 19.4N 105.7W   50 KT  60 MPH

36H  25/0600Z 20.2N 106.0W   50 KT  60 MPH

48H  25/1800Z 21.2N 106.2W   45 KT  50 MPH

72H  26/1800Z 22.7N 107.0W   40 KT  45 MPH

96H  27/1800Z 24.0N 108.4W   35 KT  40 MPH...POST-TROPICAL

120H  28/1800Z 26.0N 110.0W   30 KT  35 MPH...POST-TROP/REMNT LOW

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. Notice the Ridge forecast to be NE of Maria.

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.

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. It is impressive.

 Water Vapor Imagery

The water vapor imagery is a good guide to where precipitation is occurring.

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

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