BahaHurican's WunderBlog of 2015 Storms that Impact the Bahamas

TD 6 Forms; Weekly Outlook 22nd to 28th August, 2010

By: BahaHurican, 2:46 AM GMT on August 22, 2010

At 5 p.m. today the area of disturbed weather previously dubbed 95L was declared a tropical depression by the National Hurricane Centre. Over the next five days it is expected to track WNW to NW across the central Atlantic, and by next Thursday it is expected to be a few hundred miles NE of Puerto Rico and the Virgin Islands. Tropical Depression 6A is expected to become Tropical Storm Danielle on Sunday and a hurricane by Monday afternoon or evening.



Weather over the Bahamas, especially in the northwest, is unsettled tonight due to a westward progressing upper level low and a another ULL to our NW which is also producing stormy weather along much of the east coast of Florida.



Currently at Nassau we are experiencing downpours with thunder / lightning.

Weekly Outlook 15th to 21st August, 2010

By: BahaHurican, 10:32 PM GMT on August 15, 2010

Historical Viewpoint


This week is traditionally the week when the Atlantic basin, particularly the Main Development Region or MDR, begins to become active. Contraindications for storm formation, such as a strategically placed TUTT, with its associated ULLs, high levels of Saharan dust and associated dry air, and the placement of the ITCZ below 10N, are all on the downswing. Sea surface temperatures have warmed, tropical waves are exiting the African coast with great regularity and high enough for the Coriolis effect to induce a spinning effect. No wonder the old hurricane rhyme says "August - come they must".

Between 1851 and 2009, thirty-five storms which were active during this week eventually impacted the Bahamas. While some of them did pass through the islands between the 15th and 21st, the majority made their impact on the Bahamas the following week (22 - 28). The implication is that during this week, Bahamians should ensure their hurricane plans are in place and give more attention to tropical cyclone formation news, as tropical storm or hurricane impacts are possible within the next 10-11 days.

Current Situation

Here is a look at the most recent surface analysis for our area:




Another viewpoint comes from OPC, which shows the Northern Atlantic and is useful for observing the current location of the semi-permanent Azores-Bermuda high.



The NHC/TAFB provides the following discussion:

THE UPPER LEVEL ANTICYCLONE LOCATED OVER THE SE CONUS EXTENDS
EASTWARD TO 70W PROVIDING MUCH OF THE W ATLC WITH NE UPPER LEVEL
FLOW. TO THE EAST...AN UPPER LEVEL TROUGH AXIS EXTENDS ALONG
32N63W TO 27N68W AND SUPPORTS A STATIONARY FRONT ANALYZED ALONG
32N59W 27N70W 30N78W TO THE GEORGIA COAST NEAR 31N81W. SCATTERED
SHOWERS AND ISOLATED TSTMS ARE WITHIN 150 NM SE OF THE FRONT E
OF 70W...FROM 19N-27N BETWEEN 70W-77W. SCATTERED SHOWERS AND
TSTMS ARE OCCURRING SOUTH OF THE FRONT WHERE HIGHER INSTABILITY
IS LOCATED FROM 22N-32N BETWEEN 77W-81W.

The Bahamas Meteorology Department's Public Forecast references this stationary front, but implies that high pressure will dominate the weather here for the rest of the week.

Implications for Tropical Cyclone Activity

The two surface analysis maps draw attention to two concerns for the Bahamas / Turks and Caicos over the next week.

First, the front that is draped near the Northern Bahamas is due to lift out to the northeast, and the high is expected to build westward underneath it. By Thursday a series of weak highs are expected to line up more or less at 20N, ridging west to the Florida peninsula. The concern here is that any systems which form near the Cape Verde islands near West Africa will move westward rather than northwest, delaying any recurvature until they get much closer to the Caribbean, The Bahamas, and the US East Coast. With the 1016 MB line hovering in our territory, we must hope for the passage of another front which breaks down the high and creates a weakness to our east.

The second feature of the maps that is of note to interests in The Bahamas / Turks and Caicos is the relatively strong low pressure system currently over the Cape Verde islands. While this system is not expected to impact any land as a tropical cyclone, it does have the potential to moisten an area of the MDR that is currently filled with SAL dust and dry air, which provides an improved environment for future storms. A moister atmosphere means storms can strengthen steadily, even rapidly, without dry air entrainment interrupting the developmental process.

The reason why both of these features draw our attention is because they provide a potential path and positive environment for this wave now crossing Western Africa to reach and impact our area in the next 7 to 10 days.



While there is a fair amount of model support for this system, and while that model support implies the system will likely be a substantial one, there's still a great deal of variation in the potential landfall options. From run to run, models have targeted the Greater Antilles, The Bahamas and Florida, the east-central East US coast, or Bermuda, and many runs have shown the system heading out to sea without impacting any land.

The message for this week is WATCH and PREPARE. We can reasonably expect that the Bahamas has as good a chance as anywhere in the Atlantic basin north of 20 N to be affected by a tropical cyclone. Whether the POTENTIAL becomes the EVENTUAL remains to be seen.

Legends of the Wunderground Poll

By: BahaHurican, 1:31 PM GMT on August 13, 2010

Since things are relatively slow, I thought a "Legends of the Wunderblog" runoff might add a little joie de vivre to our Wunderblogging experience. The following events were nominated in Dr. Master's blog because they typify Wunderblog history or lore.

Legends of the Wunderground nominees in cronological order

1. Katrina 2005 "StormTop said it would hit NOLA"
2. Rita 2005 "I tried to evacuate"
3. Wilma 2005 "the definitive pinhole eye"
4. Chris 2006 "Sheared again… Naturally"
5. Ernesto 2006 "yes it is; no it's not"
6. Dean 2007 "is that cat 5 landfall????"
7. Felix 2007 "graupel in the guts"
8. Humberto 2007? "Talk about explosive cyclogenesis"
9. Karen 2007 "never say die"
10. Dolly 2008 "no closed low"
11. Fay 2008 "Florida vacation"
12. Gustav 2008 "I can fake u out"
13. Ike 2008 aka "Ike Jr."; "Beeline for South Florida! ... NOT"
14. Portlight 2008 formation "We are the Blog"
15. Marco 2008 "World's Smallest 'cane or Largest Tornado"

Now we are ready to vote on the top five legends of the blog. The main requirement is that it has to have entered the "history" or collective memory of the blog as a notable event. This is beyond simply the fact that a storm was notable for breaking a record or causing a lot of damage.

List your top FIVE picks in order from most legendary to least. If you wish, you can add a comment that explains why you feel your top pick is the most legendary blog event.

I will close the poll at midnight EDT [0400 UTC] and post results tomorrow morning.

Have fun!


============================================================

4:20 p.m. 14 Aug 2010

LEGENDS OF THE WUNDERGROUND RESULTS

First, I'd like to thank all those who participated and made this a lot of fun. Altogether 17 bloggers voted. I'm reporting my findings in three ways:
1) greatest number of votes in each category [1 - 5]
2) most popular choices [total number of votes for a particular event, regardless of category]
3) WEIGHTED results. Here I assigned a number of points for each vote based on category [1 - 5]

CATEGORY WINNERS

#1 Legend: Katrina
#2 Legend: Portlight
#3 Legend: Ike
#4 Legend: Gustav
#5 Legend: Rita

POPULARITY CONTEST

Tied for 1st KATRINA / WILMA [each received 11 total votes]
Tied for 3rd IKE / PORTLIGHT [each received 9 total votes]
5th place DEAN [with 7 total votes]

WEIGHTED RESULTS
Note: Here I assigned points from 5 to 1 for a vote in each of the categories, that is Cat 1=5 points, Cat 2=4 points and so on, with cat 5=1 point. Then I totaled the points each event received, and here are the final results of all 15 nominees in descending order.

51 votes 1. Katrina 2005 "StormTop said it would hit NOLA"
40 votes 3. Wilma 2005 "the definitive pinhole eye"
33 votes 14. Portlight 2008 formation "We are the Blog"
23 votes 13. Ike 2008 aka "Ike Jr."; "Beeline for South Florida! ... NOT"
18 votes 6. Dean 2007 "is that cat 5 landfall????"

15 votes 12. Gustav 2008 "I can fake u out"
13 votes 2. Rita 2005 "I tried to evacuate"
11 votes 7. Felix 2007 "graupel in the guts"
11 votes 11. Fay 2008 "Florida vacation"
06 votes 10. Dolly 2008 "no closed low"
05 votes 8. Humberto 2007? "Talk about explosive cyclogenesis"
04 votes 4. Chris 2006 "Sheared again… Naturally"
04 votes 15. Marco 2008 "World's Smallest 'cane or Largest Tornado"
03 votes 9. Karen 2007 "never say die"
01 votes 5. Ernesto 2006 "yes it is; no it's not"

A Climatological Perspective on the 2010 Atlantic Hurricane Season

By: BahaHurican, 1:55 AM GMT on August 12, 2010

Yesterday, 10th August, 2010, Dr. Philip Klotzbach, Research Scientist, Department of Atmospheric Science, Colorado State University, made a guest post on "Watts Up With That?", a blog run by Anthony Watts, on the topic "Atlantic Hurricane Season Analysis". I read Mr. Klotzbach's comments with interest, giving special attention to his "Table 1: La Niña years since 1950 along with the date of 2nd hurricane formation and the seasonal ACE accumulated in each year." This table references 16 La Nina years from 1950 to 2009 and gives the date of formation of the second hurricane and the seasonal ACE for each year.

The table in particular sparked my interest, and as a result all afternoon I've been futzing about with Klotzbach's table of La Nina years correlated to date of 2nd hurricane formation.


Some Interesting Observations I've Made Based on Klotzbach's Original Table

1. Only three of the seasons Klotzbach identified had a second hurricane before 11 Aug. [These were 1995, 1970, and 1956, the latter two of which were very low ACE years.]

2. 56.25% , or 9, of the La Nina seasons had above average ACE [that is, ACE above 100].

3. Only one season with an ace of over 100 had its second hurricane before 10 Aug. [Ironically that season was 1995, with its 19 storms.] Every other above average season, ACEwise, had its second hurricane form AFTER 11 Aug.


1995 was a hyperactive La Nina season.

4. The average [mean] ACE in La Nina seasons since 1950 is 129.75.

To me this suggests that La Nina seasons typicially ramp up earlier than average [average date of formation of a second hurricane is 28 Aug] but NOT before the second decade of Aug. In other words, what we're seeing is not Atypical of La Nina years in the Atlantic basin.

My Extensions of Dr. Klotzbach's Dataset

I collated some additional data relating to these 16 seasons, then looked for additional trends. I gathered information about
a) the formation date of the FINAL storm in each of these seasons,
b) the total number of named storms, and
c) the total number of major hurricanes.

Final Hurricane Formation Date

The formation date for the final storm of the selected seasons ranged from 4 Oct to 9 Dec, and the mean formation date was 3 November. 9 of the 16, or 56.5%, formed on or after 1 November. [NOTE: while I did not record dissipation dates, many storms forming after 20 Oct continued into November.] 67% of seasons with above-average ACE ended with a storm that formed after 31 Oct; the average date was 4 Nov. Again, 1995 fell into the anomalous category, with its 19th storm forming on 27 Oct.

Total Number of Named Storms

As has been presented in other research, La Nina seasons tend to have above average numbers of named storms. The average of these 16 seasons is 11.81, which can be rounded to 12. The smallest number is 8, seen in the 1956 and 1973 seasons, and of course 1995 has the largest, 19. Interestingly enough, seasons with above average ACE only averaged 0.97 more storms than the sample mean, though they did see 2.21 more storms on average than the 10.57 mean of years that had average and below average ACE. However, even storms with average and below average ACE beat the seasonal average of named storms.


The low-ACE 1973 hurricane season.

Total Number of Major Storms

For the La Nina years Kotzbach focused on, number of major hurricanes varied from 1 to 8 per season. There was a high correlation between seasonal ACE and number of major storms; average and below average seasons [seven] had a mean of 1.86 cat 3 - 5 hurricanes, while the above 100 ACE seasons averaged 5 major storms. The mean across the set was 3.86 major hurricanes per season. Only one high ACE season, 1954, had fewer than three major hurricanes, and every below 100 ACE season except 1971 and 1973 had at least two major storms.

Observations and Conclusions

1. Anybody who expects 12 - 15 named storms this year is well within the climatology. Anybody who expects 19 likely believes there are some climatologically anomolous conditions which would predispose the basin towards much higher than average activity levels, both in term of named storms and in terms of ACE.

2. We can reasonably expect the season to last beyond 1 Nov, regardless of number of named storms and / or ACE. One low ACE season had 15 named storms; another initiated its final storm on 9 Dec.

3. There seems to be no immediately obvious correlation between number of storms and number of major hurricanes. 1950 and 1973 both had 13 named storms; both had their second hurricane form on 20 Aug; both seasons ended in mid-Oct [18th and 16th respectively]. 1950 had eight majors; 1973 had one.



The 1950 season had only 13 storms, but eight of them were major hurricanes.

I'm sure there are other things to think about from this data. But it is interesting to note that five of the 7 low or average ACE years took place between 1970 and 1975...




The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

BahaHurican's WunderBlog of 2015 Storms that Impact the Bahamas

About BahaHurican

During the 2015 Atlantic hurricane season, this blog will focus on tropical systems that impact The Bahamas and Turks & Caicos Islands.

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