July Atlantic hurricane outlook

By: Dr. Jeff Masters , 12:55 PM GMT on July 13, 2012

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It's mid-July, and we have yet to see a named storm form in the Atlantic this month. The computer models are not predicting any development through at least July 20, and if we make it all the way to the end of the month without a named storm forming, it will be the first July since 2009 without a named storm. Since the current active hurricane period began in 1995, 13 of 17 years (76%) have had a named storm form during July. The busiest July occurred in 2005, when five named storms and two major hurricanes formed. These included Hurricane Dennis and Hurricane Emily--the strongest hurricanes ever observed so early in the season. Only eight major hurricanes have formed in July since record keeping began in 1851. As seen in Figure 1, most of the last half of July activity occurs in the Gulf of Mexico and waters off the Southeast U.S. coast. These type of storms form when a cold front moves off the U.S. coast and stalls out, with the old frontal boundary serving as a focal point for development of a tropical disturbance (as happened for Alberto, Beryl, Chris, and Debby in 2012.) There will be at least two cold fronts moving off the U.S. Mid-Atlantic coast over the next two weeks. The first of these fronts will push offshore around July 20, and we will need to watch the waters offshore of North Carolina for development then. Formation potential will be aided by ocean temperatures that are about 0.7°C (1°F) above average along the U.S. East Coast.


Figure 1. Tracks of all tropical storms and hurricanes 1851 - 2006 that formed July 16-31. The U.S. coast from North to Texas are the preferred strike locations. Only a few storms have formed in the tropical Atlantic and Caribbean in July. Wind shear is typically too high and SSTs too cool in July to allow African waves in the Caribbean and tropical Atlantic to develop into tropical storms. However, a few long-track "Cape Verdes" hurricanes have occurred in July, spawned by tropical waves that came off the coast of Africa. African tropical waves serve as the instigators of about 85% of all major hurricanes.


Figure 2. The seasonal distribution of Atlantic hurricane activity shows that July typically has low activity. Image credit: NHC.

Sea Surface Temperatures: slightly above average
The departure of Sea Surface Temperatures (SST) from average over the tropical Atlantic between Africa and Central America was about 0.3°C above average during June (Figure 3.) This figure has not changed much over the first two weeks of July. These temperatures are not warm enough to appreciably affect the odds of a July named storm or hurricane. The strength of the Azores-Bermuda high has been near average over the past two weeks, driving near-average trade winds. The latest 2-week run of the GFS model predicts continued average-strength trade winds through late-July, so SSTs should remain about 0.3°C above average during this period, due to average amounts of cold water mixing up from below due to the wind action on the water.


Figure 3. Sea Surface Temperature (SST) departure from average for July 12, 2012. SSTs were 0.3°C above average over the tropical Atlantic's Main Development region for hurricanes, from Africa to Central America between 10° and 20° North Latitude. Note the large region of above average SSTs along the Equatorial Pacific off the coast of South America, the hallmark of a developing El Niño episode. Image credit: NOAA/NESDIS

El Niño on the way?
For two consecutive weeks, ocean temperatures 0.5 - 0.6°C above average have been present in the tropical Eastern Pacific, which is right at the threshold for a weak El Niño episode. NOAA's Climate Prediction Center has issued an El Niño Watch, and gives a 61% chance that El Niño conditions will be present during the August - September - October peak of the Atlantic hurricane season. The likely development of a full-fledged El Niño episode means that Atlantic hurricane activity will probably be suppressed in 2012, due to the strong upper-level winds and high wind shear these events typically bring to the tropical Atlantic.


Figure 4. Sea Surface Temperature (SST) departure from average for the the equatorial Eastern Pacific (the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region"). El Niño conditions exist when the SST in this region rises 0.5°C above average. As of July 9, 2012, SSTs in the Niño 3.4 region had risen to 0.5°C above average. To be considered an "El Niño episode", El Niño conditions must occur for five consecutive months, using 3-month averages. Image credit: NOAA Climate Prediction Center.

Wind shear: above average
Wind shear is usually defined as the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude). In most circumstances, wind shear above 20 knots will act to inhibit tropical storm formation. Wind shear below 12 knots is very conducive for tropical storm formation. High wind shear acts to tear a storm apart. The jet stream has two bands of strong high-altitude winds that are currently bringing high wind shear to the Atlantic. The southern branch (subtropical jet stream) is bringing high wind shear to the Caribbean, and the northern branch (polar jet stream) is bringing high wind shear to the waters offshore of New England. This configuration often leaves a "hole" of low shear between the two branches, off the Southeast U.S. coast and over the Gulf of Mexico. The jet stream is forecast to maintain this two-branch pattern over the coming two weeks. Wind shear has been about 10 - 20% higher than average over the first two weeks of July, and is predicted to be mostly above average for the coming two weeks. This will cut down on the odds of a July storm.


Figure 5. Vertical instability over the Caribbean Sea in 2012 (blue line) compared to average (black line.) The instability is plotted in °C, as a difference in temperature from near the surface to the upper atmosphere. Thunderstorms grow much more readily when vertical instability is high. Instability has been lower than average, due to an unusual amount of dry air in the atmosphere, reducing the potential for tropical storm formation. Image credit: NOAA/NESDIS/CIRA.

Dry air: above average
As seen in Figure 5, there has been an unusual amount of dry, stable air in the Caribbean this year creating low levels of vertical instability. This has occurred due to a combination of dry air from Africa, and upper-atmosphere dynamics creating large areas of sinking air that dry as they warm and approach the surface. The Gulf of Mexico and tropical Atlantic between the coast of Africa and the Lesser Antilles have also seen low vertical instability this summer. June and July are the peak months for dry air and dust coming off the coast of Africa, and the Saharan dust storms have been quite active over the past two weeks. Expect dry air to be a major deterrent to any storms that try to form in the tropical Atlantic during July.

Steering currents: average
The predicted steering current pattern for the next two weeks is a typical one for July. We have an active jet stream bringing many troughs of low pressure off the East Coast of the U.S. These troughs are frequent enough and strong enough to recurve any tropical storms or hurricanes that might penetrate north of the Caribbean Sea. Steering current patterns are predictable only about 3 - 5 days in the future, although we can make very general forecasts about the pattern as much as two weeks in advance. There is no telling what might happen during the peak months of August, September, and October--we might be in for a repeat of the favorable 2010 and 2011 steering current pattern, which recurved most storms out to sea--or the unfavorable 2008 pattern, which steered Ike and Gustav into the Gulf of Mexico.

Summary: a below average chance of a July tropical storm
Given that none of the computer models are forecasting tropical storm formation in the coming seven days, SSTs are only slightly above average, and wind shear and vertical stability are above average, I'll go with a 30% chance of a named storm forming in the Atlantic during the remainder of July.


Figure 6. Hurricane Emilia over the Eastern Pacific at 20:35 UTC July 10, 2012. At the time, Emilia was a Category 3 hurricane with 125 mph winds. Emilia peaked earlier in the day as a Category 4 storm with 140 mph winds--the strongest hurricane in the East Pacific so far in 2012. Image credit: NASA.

An active Eastern Pacific hurricane season
It's been a very active start to the Eastern Pacific hurricane season, where we've already had six named storms, four hurricanes, and three intense hurricanes. A typical season has 4 named storms, 2 hurricanes, and 0 intense hurricanes by July 14. The formation of Tropical Storm Fabio on July 12 marks the 4th earliest formation of the Eastern Pacific's season's sixth storm. The record is held by the year 1985, when the season's sixth storm formed on July 2. Record keeping began in 1949.

Have a great weekend, everyone, and I'll be back Monday with a new post.

Jeff Masters

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Orange


McLewis


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Quoting GeorgiaStormz:


by SEP they average just above 1 and if you take into account the down turn you get our result

?
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Quoting nrtiwlnvragn:


NMME forecasts would disagree:




by SEP they average just above 1 and if you take into account the down turn you get our result
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Quoting GeorgiaStormz:


oh yeah, i forgot, we still our CME late tonight/tomorrow morning

MUAAHHHAHHAHHHAHH.
I feel happy today, is that good?
Lol.If you believe in superstition yep :).
Member Since: August 14, 2010 Posts: 10 Comments: 17487
Quoting TropicalAnalystwx13:

I agree. Nothing above 1.0 °C.


NMME forecasts would disagree:


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Quoting washingtonian115:
We'll see what the sun says today :).


oh yeah, i forgot, we still our CME late tonight/tomorrow morning

MUAAHHHAHHAHHHAHH.
I feel happy today, is that good?
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Quoting MTWX:
Massive landslide in Alaska sweeps over glacier


Thanks for the info. More in depth reports with good pics on Dave's landslide blog. And a new landslide with (probably) four fatatlities unfortunately happenend in Canada.

Link to Dave's Blog.
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Quoting washingtonian115:
The hater?. Don't be so quick.Sometimes the atmosphere can change on a dime.


into a quarter?
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Quoting GeorgiaStormz:
Happy 3rd Friday the 13th

This is the 3rd one this year, all of which were 13 weeks apart.
Let the 2012 destruction begin XD
We'll see what the sun says today :).
Member Since: August 14, 2010 Posts: 10 Comments: 17487
Happy 3rd Friday the 13th

This is the 3rd one this year, all of which were 13 weeks apart.
Let the 2012 destruction begin XD
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Quoting StormTracker2K:
I see the behind scenes guy Tigerosee is on.
The hater?.
Quoting GeorgiaStormz:


i am sure it wont
Don't be so quick.Sometimes the atmosphere can change on a dime.
Member Since: August 14, 2010 Posts: 10 Comments: 17487
Quoting islander101010:
watching.the.area.just.north.of.the.yucatan..band in g.starting.to.show


dont worry about it.
Its just a blob
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I see the behind scenes guy Tigerosee is on.
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There's Fabio's eye!
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watching.the.area.just.north.of.the.yucatan..bandin g.starting.to.show
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It looks like where not going to have to worry this year with the hurricanes way things are shaping up, and from what I'm reading. We deserve a worry free summer.

Sheri
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Quoting StormTracker2K:
Ernesto?




ernestlyno
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92. MTWX
Massive landslide in Alaska sweeps over glacier
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Quoting washingtonian115:
maybe the storm never materializes.


i am sure it wont
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Quoting TropicalAnalystwx13:
em ADDITIONAL WEAKENING IS INDICATED...AND EMILIA IS FORECAST
TO BECOME A REMNANT LOW IN A COUPLE OF DAYS...OR EARLIER.



All because you said it would be very slow to wind down it falls apart much faster....
but then again, its rapid demise was unexpected to me too
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On Mid July of 1997 it was already a strong El Nino.



Right now.

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Quoting StormTracker2K:


Shear could be problem once it enters the Caribbean. Usually the eastern Caribbean is a tough place to get developement this time of year and sustain a tropical cyclone during the month of July.
I won't be forecasting what shear could be like at that time.Who knows maybe a anticyclone will form to protect it maybe the storm never materializes.We'll just have to see what conditions are at that time.
Member Since: August 14, 2010 Posts: 10 Comments: 17487
Quoting TropicalAnalystwx13:

I agree. Nothing above 1.0 °C.


i agree, but by winter i am thinking a 1.5-2.5 peak

SNOW!!!!????
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Quoting TropicalAnalystwx13:

It took a long time to get to 0.5C and waters in the equatorial Pacific have taken a big hit over the past two weeks.


Remember though we were at -1c as we were coming out of a strong La-Nina earlier in the year. No question as Doc said El-Nino will be fully in charge come August but the next question will be how strong? That is where the big question is right now and one that no one has a concrete answer for. So we'll see!
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TROPICAL STORM FABIO DISCUSSION NUMBER 6
NWS NATIONAL HURRICANE CENTER MIAMI FL EP062012
800 AM PDT FRI JUL 13 2012

RECENT SSMI AND SSMIS DATA INDICATE THAT FABIO HAS DEVELOPED A
CLOSED RING OF DEEP CONVECTION...AND AN EYE-LIKE FEATURE HAS
BEEN OBSERVED INTERMITTENTLY IN INFRARED IMAGERY. DVORAK ESTIMATES
AT 1200 UTC FROM TAFB AND SAB REMAINED AT T3.0...OR 55 KT...AND THE
UW-CIMSS ADT JUMPED TO ABOUT 75 KT WHEN AN ADJUSTMENT FOR THE
MICROWAVE DATA WAS APPLIED. THE INITIAL INTENSITY IS BEING SET AT
60 KT FOR NOW...AND FABIO APPEARS TO BE ON THE VERGE OF BECOMING A
HURRICANE.

THE MICROWAVE DATA HELPED TO MORE ACCURATELY LOCATE THE LOW-LEVEL
CENTER...AND FABIO IS ESTIMATED TO BE MOVING 300 DEGREES AT 9 KT.
A DEVELOPING MID-/UPPER-LEVEL LOW OVER SOUTHERN CALIFORNIA IS
BEGINNING TO ERODE THE SUBTROPICAL RIDGE TO THE NORTH OF FABIO...
AND A DIGGING SHORTWAVE TROUGH NEAR THE OREGON COAST SHOULD
HELP TO AMPLIFY THE TROUGH NORTH OF THE CYCLONE IN THE NEXT FEW
DAYS. THE TRACK GUIDANCE REMAINS IN GOOD AGREEMENT THAT FABIO WILL
ULTIMATELY TURN NORTH-NORTHWESTWARD TOWARD THE TROUGH BY DAY 5.
THE NEW NHC FORECAST IS VERY CLOSE THE ECMWF AND THE MODEL CONSENSUS
TVCE AND IS BASICALLY AN UPDATE FROM THE PREVIOUS ADVISORY.

NORTHEASTERLY SHEAR IS STILL AFFECTING FABIO...BUT IT DOES NOT
APPEAR TO BE STRONG ENOUGH TO KEEP THE CYCLONE FROM GRADUALLY
STRENGTHENING. ALTHOUGH RAPID INTENSIFICATION CANNOT BE RULED
OUT...THE SHIPS RI INDEX FOR A 30-KT INCREASE IN WINDS OVER THE
NEXT 24 HOURS IS ONLY AT 2 PERCENT. THE OFFICIAL INTENSITY
FORECAST WILL THEREFORE NOT SHOW RAPID INTENSIFICATION...BUT
STRENGTHENING IS STILL EXPECTED BEFORE FABIO REACHES COLDER WATER
IN ABOUT 36 TO 48 HOURS.

FORECAST POSITIONS AND MAX WINDS

INIT 13/1500Z 15.0N 110.6W 60 KT 70 MPH
12H 14/0000Z 15.6N 111.8W 65 KT 75 MPH
24H 14/1200Z 16.1N 113.4W 75 KT 85 MPH
36H 15/0000Z 16.4N 115.0W 70 KT 80 MPH
48H 15/1200Z 16.8N 116.4W 65 KT 75 MPH
72H 16/1200Z 18.5N 119.0W 50 KT 60 MPH
96H 17/1200Z 20.5N 120.5W 35 KT 40 MPH
120H 18/1200Z 23.0N 121.5W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
FORECASTER BERG
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No GOM
No CV

just like i said
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Quoting washingtonian115:
That high is sending it right into the caribbean.The caribbean has some of the highest TCHP in the basin.Hope shear is strong enough to keep it at bay.



Cent/NE GOM is gaining Vorticity

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TROPICAL STORM EMILIA DISCUSSION NUMBER 24
NWS NATIONAL HURRICANE CENTER MIAMI FL EP052012
800 AM PDT FRI JUL 13 2012

MOST OF THE CONVECTION ASSOCIATED WITH EMILIA IS GONE...WITH THE
EXCEPTION OF A SMALL CELL SOUTH OF THE CENTER. HOWEVER...I WILL NOT
BE SURPRISED IF ADDITIONAL CELLS DEVELOP INTERMITTENTLY DURING THE
NEXT DAY OR TWO AS THE CYCLONE GRADUALLY WEAKENS. SINCE EMILIA WAS A
STRONG HURRICANE...IT IS ASSUMED THAT IT WILL TAKE A WHILE FOR THE
WINDS TO SPIN DOWN...AND THE INTENSITY IS STILL ESTIMATED TO BE 55
KNOTS. ADDITIONAL WEAKENING IS INDICATED...AND EMILIA IS FORECAST
TO BECOME A REMNANT LOW IN A COUPLE OF DAYS...OR EARLIER.

EMILIA IS MOVING TOWARD THE WEST OR 275 DEGREES AT 12 KNOTS STEERED
BY THE LOW-LEVEL FLOW. NO IMPORTANT CHANGES IN TRACK OR FORWARD
SPEED ARE ANTICIPATED THROUGH THE FORECAST PERIOD. THIS IS
CONSISTENT WITH GUIDANCE WHICH SHOWS A WEAKENING CYCLONE OR A
REMNANT LOW PROGRESSING WESTWARD FOR THE NEXT SEVERAL DAYS.


FORECAST POSITIONS AND MAX WINDS

INIT 13/1500Z 15.6N 126.0W 55 KT 65 MPH
12H 14/0000Z 15.7N 127.8W 40 KT 45 MPH
24H 14/1200Z 16.0N 130.3W 35 KT 40 MPH
36H 15/0000Z 16.2N 133.2W 30 KT 35 MPH
48H 15/1200Z 16.3N 136.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 16/1200Z 16.5N 141.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 17/1200Z 16.5N 147.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 18/1200Z 16.5N 152.0W 20 KT 25 MPH...POST-TROP/REMNT LOW

$$
FORECASTER AVILA
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............great day here for the vacationers around tampa bay and the beaches
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Quoting StormTracker2K:


Remember September/October is still 2 to 3 months away and were at .05C right now so it wouldn't take long to get to 1.0C mark.

It took a long time to get to 0.5C and waters in the equatorial Pacific have taken a big hit over the past two weeks. As StormChaser2007 stated yesterday, it'll take several weeks just to recover from that, let alone continue to strengthen afterwards.
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Quoting washingtonian115:
That high is sending it right into the caribbean.The caribbean has some of the highest TCHP in the basin.Hope shear is strong enough to keep it at bay.


Shear could be problem once it enters the Caribbean. Usually the eastern Caribbean is a tough place to get developement this time of year and sustain a tropical cyclone during the month of July.
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Quoting StormTracker2K:


Remember September/October is still 2 to 3 months away and were at .05C right now so it wouldn't take long to get to 1.0C mark.
Remember back in February when people said we'll have a full blown El nino by late June and as you and I and everyone else can see that has not materialized.Kelvin waves don't seem to be transporting warm water so far.We'll see what it looks like for the end of August.But i'm still forecasting a weak El nino.
Member Since: August 14, 2010 Posts: 10 Comments: 17487
Quoting StormTracker2K:
Ernesto?


That high is sending it right into the caribbean.The caribbean has some of the highest TCHP in the basin.Hope shear is strong enough to keep it at bay.
Member Since: August 14, 2010 Posts: 10 Comments: 17487
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Quoting TropicalAnalystwx13:

I agree. Nothing above 1.0 °C.


Remember September/October is still 2 to 3 months away and were at .05C right now so it wouldn't take long to get to 1.0C mark.
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Ernesto?


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Quoting TropicalAnalystwx13:

I agree. Nothing above 1.0 °C.
In order for that to happen El nino would have to form more at a rapid pace and it seems to be taking it's sweet time.
Member Since: August 14, 2010 Posts: 10 Comments: 17487
Quoting washingtonian115:
I don't think el nino will be that strong by September and October.More in the weak range.



maybe, maybe not.....
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Quoting washingtonian115:
I don't think el nino will be that strong by September and October.More in the weak range.

I agree. Nothing above 1.0 °C.
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Quoting JeffMasters:


I've learned not to make forecasts beyond 10 days! The odds of being wrong are too high.

Jeff Masters


Nice!
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Quoting StormTracker2K:



It's just a glitch in the overall progression of El-Nino so no worries as El-Nino will be in the strong range by September or October.

I don't think el nino will be that strong by September and October.More in the weak range.
Member Since: August 14, 2010 Posts: 10 Comments: 17487
Quoting Tropicsweatherpr:
The daily SOI continues for a 6th day in a row in positive.

Link



It's just a glitch in the overall progression of El-Nino so no worries as El-Nino will be in the strong range by September or October.

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Thanks for the update, Dr. Masters. The tropical Atlantic looks inactive. Let's hope it stays that way -- or at least any big threats stay offshore.
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Fabio still at T3.5
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........................................some good news ahead for NW Texas
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Quoting Tropicsweatherpr:
The daily SOI continues for a 6th day in a row in positive.

Link

According to the link,
Daily values are not the SOI but contribute to the calculation of the monthly SOI.
Although the daily SOI is running positive for six days straight, the 1-month SOI is -7.16, and the the 3-month SOI is -3.43. Just in case you didn't notice.
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The top 4 connected kinked lines represent 4days of Emilia's path since it became a hurricane*.

The bottom 3 connected kinked lines represent the 3days of Daniels's path as a hurricane.

Note how Emilia has pret much fallen into the trough carved by Daniel's passage.

* As of the 13July6amGMT ATCF, Emilia became a TropicalStorm again on the final dot of the 4th day.
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Quoting TropicalAnalystwx13:

Fabio is strengthening faster than they thought.

Really? I thought it wasn't. My mistake. Thanks for noticing that. Actually I just checked the archive for Fabio; at the first advisory, NHC was underestimating the wind speed; but after that, they correctly predicted 65 mph.
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.