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posted on 17 September 2017

Extreme Concern about Maria: 17Sep2017 - Update

Written by Sig Silber

This post has been updated. You can access the new post at Extreme Concern about Maria: 17Sep2017 - Update 2

2:00 PM EDT Sept 17, 2017  An aircraft flight a day beats satellite data any day of the week. The Jose flight results are in and we are awaiting the results of today's Maria flight. Also the European forecasting model is more reliable than the U.S. forecasting model. Those are the facts of life. Jose appears to be hyped and the best advice is to not go swimming especially off of Cape Cod and observe rip tide rules. Maria is of more concern but there is time for it to change its track.

Special Landing Graphic for Possible Hurricane Maria

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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. 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

Note Tropical Storm Maria. It is a real threat!!!!!!!!!!

And now the Pacific. 

Eastern Tropical Pacific 

Norma is no longer much of a threat even for Baja California. Otis is moving to the west. Only Jose and Maria are of concern other than for shipping.

The two most dangerous storms right now are in the Atlantic.

We start our Report with currently Tropical Storm Maria, which now appears to be the main threat to life and property and soon. Where you see an "M" on a track map that means a Hurricane of Category 3 or higher. Predictions four days out are not highly reliable but a prediction of an "M"  storm directly on Puerto Rico can not be ignored.

Tropical Depression 15

And the Discussion

Tropical Storm Maria Discussion Number 5 NWS National Hurricane Center Miami FL 1100 AM AST Sun Sep 17 2017

The cloud pattern has not changed much since the last advisory. There appears to be a dry slot working into the western side of Maria, and the low-level circulation seems to be peaking out from under the western side of a persistent CDO feature.  Dvorak estimates are unchanged from six hours ago, so the initial intensity is held at 55 kt.  An Air Force Reserve Hurricane Hunter aircraft will be investigating Maria this afternoon.

Maria continues to move west-northwestward, or 290/13 kt, and that trajectory is expected to continue at least for the next four days while a mid-level high is centered over the western Atlantic Ocean. However, the track guidance has generally slowed down since the high is not very expansive or strong, and the new NHC track forecast follows that trend, ending up a little slower than the previous forecast.  The official forecast also continues to hedge toward the southern side of the track guidance envelope, closest to the ECMWF and HCCA models, which have been doing very well this hurricane season.

Until the reconnaissance aircraft investigates Maria, the initial intensity will be a little uncertain.  Regardless, the storm is within an environment of very low shear and over sea surface temperatures around 29 degrees Celsius, so steady strengthening is expected during the next few days.  Due to this seemingly ideal environment, the NHC intensity forecast is higher than the statistical-dynamical guidance and closely follows HCCA and the ICON intensity consensus through the entire forecast period.  Maria is likely to become a hurricane later today and could become a major hurricane in 2 to 3 days.  No major changes to the intensity forecast were necessary compared with the previous cycle, and I'd rather wait anyway until we have a better handle on Maria's intensity and structure.


1. Maria is expected to strengthen and affect portions of the Leeward Islands as a hurricane early this week, bringing dangerous wind, storm surge and rainfall hazards.  Hurricane and tropical storm warnings have been issued for portions of the Leeward Islands, and these warnings will likely be extended northward and westward later today and tonight.

2. Maria could also affect the British and U.S. Virgin Islands and Puerto Rico by mid week as a dangerous major hurricane, and hurricane watches could be issued for these islands as early as tonight.  Interests in these areas should monitor the progress of Maria and follow any advice given by local officials.


INIT  17/1500Z 13.5N  56.2W   55 KT  65 MPH

12H  18/0000Z 14.1N  57.7W   65 KT  75 MPH

24H  18/1200Z 14.8N  59.3W   75 KT  85 MPH

36H  19/0000Z 15.5N  60.7W   85 KT 100 MPH

48H  19/1200Z 16.1N  62.0W   95 KT 110 MPH

72H  20/1200Z 17.3N  64.7W  110 KT 125 MPH

96H  21/1200Z 18.5N  67.5W  105 KT 120 MPH

120H  22/1200Z 20.0N  69.5W  100 KT 115 MPH

We observed a slight change in the track forecast after Puerto Rico. That will be of interest as this storm moves closer and more information becomes available.

Here is the current Track Map for Jose. 

Tropical Storm Jose

Notice Jose is projected to go out to sea. The issue is when? Does it take a small move west first? What about Nova Scotia and Cape Cod? The most recent discussions from NHC are optimistic.  The risk to Nova Scotia seems to have been reduced. Cape Cod will be wet. We will pay close attention to the NHC Discussion updates.

Jose Discussion

Hurricane Jose Discussion Number 49 NWS National Hurricane Center Miami FL 1100 AM EDT Sun Sep 17 2017

The Air Force Hurricane Hunters have been investigating Jose this morning and found flight-level winds of 86 kt, SFMR surface winds of 89 kt, and a minimum pressure of 967 mb.  Based on these data, the initial wind speed is raised to 80 kt for this advisory. Even though the winds are stronger than earlier, the hurricane does not have an improved appearance in satellite images.  In fact, the Air Force meteorologist onboard the aircraft mentioned that the inner core of Jose is asymmetric and the overall appearance is lopsided.

Jose is expected to be in an environment of strong southwesterly wind shear while it is over the warm Gulf Stream waters during the next couple of days.  Although the shear is forecast to lessen beyond that time, the hurricane will likely have crossed the north wall of the Gulf Stream by then, where the waters are much cooler. These environmental conditions favor a slow weakening trend during the next several days, and that is reflected in the NHC intensity forecast.  It should be noted, however, that despite the expected weakening, the models suggest that Jose's outer wind field will expand, which is typical for tropical cyclones that move into the mid-latitudes.

The hurricane is moving northward at 8 kt on the west side of a subtropical ridge.  This motion is expected to continue for 2 to 3 days while the steering pattern persists.  Thereafter, a trough currently over central Canada is expected to move eastward and should cause Jose to turn to the northeast and east at a slow forward speed in the 3- to 5-day time frame.  The NHC track forecast has been shifted slightly to the left of the previous one, mainly because of the more westward initial position.


1. The center of Jose is forecast to pass well east of the North Carolina coast on Monday, and tropical-storm-force winds are currently expected to remain offshore of the North Carolina Outer Banks. However, an additional increase in the size of the storm or a westward adjustment in the track forecast could bring tropical storm conditions closer to the Outer Banks, and interests there should monitor the progress of Jose through Monday.

2. While the center of Jose is currently forecast to remain offshore of the U.S. coast, the large cyclone could cause some direct impacts from Virginia northward to New England, and any deviation to the left of the NHC forecast track would increase the likelihood and magnitude of those impacts.  Interests along the U.S. east coast from Virginia to New England should monitor the progress of Jose through the next several days.  Tropical storm watches could be required for a portion of this area later today.

3. Swells generated by Jose are affecting Bermuda, the Bahamas, and much of the U.S. east coast. These swells are likely to cause dangerous surf and rip current conditions for the next several days in these areas.


INIT  17/1500Z 31.0N  71.9W   80 KT  90 MPH

12H  18/0000Z 32.0N  71.8W   80 KT  90 MPH

24H  18/1200Z 33.6N  71.8W   75 KT  85 MPH

36H  19/0000Z 35.2N  71.8W   70 KT  80 MPH

48H  19/1200Z 36.7N  71.8W   70 KT  80 MPH

72H  20/1200Z 39.6N  70.4W   60 KT  70 MPH

96H  21/1200Z 40.0N  67.5W   55 KT  65 MPH

120H  22/1200Z 39.5N  65.5W   50 KT  60 MPH...POST-TROPICAL

This shows the loop de loop of Jose pretty well. It is not that unusual but makes long-term forecasting difficult. Also you can see that the track of Jose was just far enough north to avoid significant impacts in the Antilles.

Jose loop de loop

Now Norma.

Tropical Storm Norma


We no longer consider Norma to be a significant threat since NHC continues to report that it is turning towards Baja as it gets further away.

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. The High north of Jose remains of interest. But it appears to be out of position to have much impact.

Some of the graphics below show the two storms of most interest. Other graphics will be more relevant for Jose as it moves north and comes into view.

Day 1 Forecast Map

Day 2 Forecast

This is a Day 2 Forecast.

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 now very relevant  as one can see three storms 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 it will show up in the September 18 Report. You can already see a preliminary precipitation QPF for Jose. It is mostly offshore and now. Cape Cod may be impacted. .

 Water Vapor Imagery

The water vapor imagery is a good guide to where precipitation is occurring. You can not see Jose and Norma. One might even conclude that they see water vapor from Norma impacting Texas but not to a significant extent.

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

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