Written by Sig Silber
Harvey 10PM CDT Monday Aug 28, 2017: 36 Hours Before Storm Heads North and Dies: Update Viewable Just After you Click “Read More”
Our monthly report on seasonal outlook updates normally consists of two parts. First we report on the new NOAA outlook and compare it to the prior NOAA Outlook and then in Part II we compare the new NOAA outlook to the new JAMSTEC outlook which not only covers Alaska and CONUS but the World. In our report published on August 19, we were unable to compare the NOAA and JAMSTEC outlooks because JAMSTEC was late. The next day they posted but it was not possible to do more than report on their Nino 3.4 forecast which differed dramatically from the NOAA Nino 3.4 forecast. In this report, we present what normally would be Part II of our monthly report, namely the comparison of the NOAA and JAMSTEC forecasts.
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Tropical Storm Harvey Discussion Number 35 NWS National Hurricane Center Miami FL 1000 PM CDT Mon Aug 28 2017
The center of Harvey has been moving east-southeastward over the extreme western Gulf of Mexico this evening. Although there is no deep convection near the center of Harvey, thunderstorm activity has continued to increase well north of the center, along the immediate northwest Gulf Coast and has spread inland over the Greater Houston area, worsening the catastrophic flooding situation. Another band of heavy rainfall is moving inland over portions of southern and southwestern Louisiana. Widespread rainfall totals of 30 to 36 inches have been observed in southeastern Texas and the Houston Metropolitan Area. Storm totals could reach 50 inches in some locations, which would be historic for the area.
A NOAA National Ocean Service observing site near Matagorda Bay has continued to report sustained tropical-storm-force winds this evening, and data from this and other nearby stations still support an initial intensity of 40 kt. Given the current structure of the cyclone and the lack of convection near the center, little change in strength is expected while Harvey moves over the northwestern Gulf of Mexico. After landfall in about 36 hours, gradual weakening should occur as the circulation moves farther inland.
Harvey has been moving east-southeastward or 120/3 kt. The storm is forecast to turn northeastward, then north-northeastward over the next couple of days as a ridge to the northwest of the system weakens and Harvey is steered around the western side of a ridge over the eastern Gulf of Mexico. The track guidance has shifted slightly eastward and the new NHC track has been adjusted in that direction.
Key Messages:
1. Ongoing catastrophic and life-threatening flooding will continue across southeastern Texas. Additional rainfall accumulations of 10 to 20 inches are expected across the upper Texas coast, with isolated storm totals as high as 50 inches. Please heed the advice of local officials. Do not attempt to travel if you are in a safe place, and do not drive into flooded roadways. Refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard. A summary of rainfall totals compiled by the Weather Prediction Center can be found at: www.wpc.ncep.noaa.gov/discussions/nfdscc1.html [Editor’s Note: Click Here to Read]
2. The flood threat has spreading farther east into Louisiana. Additional rainfall amounts of 10 to 20 inches are expected in southwestern Louisiana, with rainfall amounts of 5 to 15 inches expected in south-central Louisiana. Rainfall amounts of 5 to 10 inches are expected in southeast Louisiana and coastal Mississippi and Alabama. Please heed the advice of local officials and refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard in these areas.
3. While Tropical Storm Warnings have been extended eastward along the coast of Louisiana and a Storm Surge Watch has been issued, the impacts of winds and storm surge are expected to be secondary compared to that of the rains.
FORECAST POSITIONS AND MAX WINDS [Editor’s Note: Looks like two days of have precipitation and the this storm finally moves inland]
INIT 29/0300Z 28.2N 95.3W 40 KT 45 MPH
12H 29/1200Z 28.1N 95.0W 40 KT 45 MPH
24H 30/0000Z 28.5N 94.5W 40 KT 45 MPH
36H 30/1200Z 29.5N 94.0W 40 KT 45 MPH
48H 31/0000Z 30.7N 93.4W 35 KT 40 MPH…INLAND
72H 01/0000Z 33.4N 91.9W 30 KT 35 MPH…INLAND
96H 02/0000Z 35.5N 90.0W 25 KT 30 MPH…INLAND
120H 03/0000Z 38.0N 86.5W 20 KT 25 MPH…POST-TROP/INLAND
The most current information on Harvey can be found here.
Now we begin our comparison of the NOAA and JAMSTEC Forecasts (Focus on next nine months i.e. three seasons)
Part I of our Monthly Seasonal Outlook Update (published on August 20, 2017) which focused on the NOAA forecast and compared it to the previous NOAA forecast can be accessed by clicking here.
Below is the July 1 and August 1 JAMSTEC Nino 3.4 forecasts side by side with the older forecast on the left and newly issued forecast on the right. The Nino 3.4 index is the most widely used measurement to predict the expected phase of ENSO. +0.5C and above suggests El Nino and -0.5C and below suggests La Nina.
Here is the NOAA forecast for the Nino 3.4 Index.
Below is a quick summary of the temperature and precipitation forecasts for three time periods and from left to right the NOAA forecast for Alaska and CONUS (the contiguous mid-latitude U.S), then JAMSTEC for North America (which includes Canada and Northern Mexico), and then JAMSTEC for Europe and surrounding areas. Larger graphics are provided later in the report but I have not that for Europe as the map shown is quite understandable in the size shown
This presentation of the key graphics is kind of a tease to keep you reading but you can see the evolution of the weather pattern through Fall, Winter and into Spring. For some readers, these two sets of summary graphics may be all the information they wish to look at and that is fine. Others have an interest in other parts of the World and may find some value in the commentary that I provide.
Temperature
Season | NOAA Alaska Plus CONUS | JAMSTEC North America | JAMSTEC Europe |
Fall SON 2017 Temp | |||
Winter DJF 2017/2018 Temp | |||
Spring MAM 2018 Temp |
Precipitation
Season | NOAA Alaska Plus CONUS | JAMSTEC North America | JAMSTEC Europe |
Fall SON 2017 Precip | |||
Winter DJF 2017/2018 Precip | |||
Spring MAM 2018 Precip |
A note about terminology; the deviations from climatology/normal are color coded but also labeled “A” for more than normal and “B” for less than normal. The area designated EC means Equal Chances of being more or less than normal. JAMSTEC relies on their color coding. In my comments I have used EC to cover all the situations where a clear anomaly is not shown.
Now the Comparison of the NOAA and JAMSTEC Forecasts.
JAMSTEC works in three-month intervals which correspond to seasons and does not change the selection of months each time they update but does so every three months. So we have SON 2017, DJF 2017-2018, and MAM 2018 to work with from JAMSTEC and the same three-month periods are available from NOAA. So everything lines up very nicely this month. I show the NOAA Maps first followed by the JAMSTEC maps. I extract North America from the Worldwide JAMSTEC map and use that to compare with the NOAA Maps. I also extract and enlarge Europe including parts of North Africa and Western Asia form the Worldwide JAMSTEC maps.
SON 2017
Temperature
NOAA SON 2017
And here is the SON temperature forecast for North America that I extracted from the JAMSTEC World Forecast
And now the JAMSTEC WORLD FORECAST (for this graphic my comments are mostly related to areas other than Alaska and CONUS as those comments appear with the graphics above)
Precipitation
NOAA SON 2017
And here is the SON 2017 Precipitation Forecast for North America that I extracted from the JAMSTEC World Forecast.
JAMSTEC WORLD FORECAST
DJF 2017/2018
Temperature
NOAA DJF 2017 – 2018
And here is the DJF 2017 – 2018 Temperature Forecast for North America that I extracted from the JAMSTEC World Forecast
JAMSTEC WORLD FORECAST
Precipitation
NOAA DJF 2017 – 2018
And here is the DJF 2017 – 2018 Precipitation Forecast for North America that I extracted from the JAMSTEC World Forecast
JAMSTEC WORLD FORECAST
MAM 2018
Temperature
NOAA MAM 2018
And here is the MAM 2018 Temperature Forecast for North America that I extracted from the JAMSTEC World Forecast
JAMSTEC WORLD FORECAST
Precipitation
NOAA MAM 2018
And here is the MAM 2018 Precipitation Forecast for North America that I extracted from the JAMSTEC World Forecast
JAMSTEC WORLD FORECAST
Conclusion
Both forecasts are based on ENSO being primarily Neutral. But the winter bias of JAMSTEC is near El Nino and the winter bias of NOAA is a near La Nina or possibly even La Nina Conditions. That adds up re the Nino 3.4 Index to a difference of close to 1C which if it was starting from pure Neutral would be either an El Nino or La Nina. As it is the two deviations from Nino 3.4 = 0 are of opposite signs so both forecasts are for ENSO Neutral Conditions for January 2018 but they are biased in different directions so this produces different forecasts. In Spring the bias is similar in both forecasts but the magnitudes are different. So we are dealing with a complex situation of differences between the two Nino 3.4 Index forecasts.
One value of doing this sort of analysis is that as the projected value of Nino 3.4 changes we have the basis for extrapolating between these two sets of forecast maps if the Nino 3.4 forecasts come closer together. If they become farther apart, it may still be possible to make some reasonable guesses as to how this will impact weather. Of course on September 21, NOAA will release a new set of maps and two days later we should be posting our analysis of their new maps and hopefully also JAMSTEC will be on time with their maps.
Some Housekeeping Issues.
The next Regular Weekly Weather and Climate Report will be published on August 28. If you are reading this Update Report and wish to transfer to the Current Weather and Climate Report, Click Here for the list of Weather Posts. That link takes you to the archive of all weather articles written by Sig Silber so you can if the new Weekly Weather Report has been published go there or back to an earlier report but please keep in mind that the graphics in earlier reports in some cases auto-update and the text may no longer apply to the graphics shown. Remember, if you leave this page to visit links provided in this article, you can return by hitting your “Back Arrow”, usually top left corner of your screen just to the left of the URL box.