African disturbance 92L could develop into tropical depression

By: Dr. Jeff Masters , 6:55 PM GMT on July 01, 2008

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A strong tropical wave (Invest 92L) moved off the coast of Africa last night, south of the Cape Verde Islands. This low has the potential to develop into a tropical depression late this week as it moves westwards at 15-20 mph. The low is under about 10 knots of wind shear, which is favorable for development. Sea Surface Temperatures are about 28°C, which is about 2-3°C above average for this date, and well above the 26°C threshold for tropical storm formation. There is not much African dust or dry air near the storm, but so far the low has not been able to generate much heavy thunderstorm activity. The low has plenty of spin, and has developed some broad, curved bands that are a sign of organization. I can't really find any negatives for development, except for climatology--there has never been a tropical depression that has formed east of 34° W longitude in the first half of July (see the first image I posted in yesterday's July Atlantic hurricane outlook). NHC is giving a low chance (less than 20%) that 92L will develop into a tropical depression by Thursday afternoon. Given the system's current disorganization, that's a reasonable forecast. However, all the models are developing this system into a tropical depression by late this week, and I think that the odds rise to a 50% chance of a tropical depression by Saturday. Wind shear is expected to remain low, and the waters will stay warm (above 26°C) for the next 2-3 days of 92L's life.


Figure 1. Latest satellite image of Invest 92L.

2008 African dust forecast
According to an experimental dust forecast by Amato Evan of the University of Wisconsin's Cooperative Institute for Meteorological Satellite Studies, 2008 should have fairly normal levels of African dust activity, similar to what was seen in 2007. This is a change from 2004, 2005, and 2006, which had fairly low levels of dust activity. This lack of dust resulted in 0.2°C less cooling of the eastern Atlantic Sea Surface Temperatures in 2004, 2005, and 2006 compared to 2007. High levels of dust block sunlight, leading to cooling of the sea surface.

Jeff Masters

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1004. TheTracker08
12:01 AM GMT on October 28, 2008
i cant wait, here we go, paloma!!!!
1003. PSLHokie
2:32 AM GMT on July 03, 2008
For whoever asked about vorticity

VORTICITY - is a measure of fluid rotation as it is translating. Its a mathematical way to break out rotation of a fluid from the translation. The formulation for vorticity in a 2-D field is
omega= (1/2) (d(phi)/ dt), where omega is vorticity, and d(phi)/dt is the change in angular position with respect to time.

Hope this makes sence....

Scott
1002. reedzone
1:49 PM GMT on July 02, 2008
It's great to finally be a wunderground blogger. I'm also known as allan on flhurricane. Great to meet you Nash and everyone else plus Drakeon, StormW, and Ike :)
Member Since: July 1, 2008 Posts: 13 Comments: 7396
1001. catastropheadjuster
1:41 PM GMT on July 02, 2008
New Blog
Member Since: August 24, 2006 Posts: 21 Comments: 3678
1000. TampaSpin
1:41 PM GMT on July 02, 2008
995. Nolehead 9:38 AM EDT on July 02, 2008
kman, that spin is still there jsut west of the islands...still have that same feeling?


I was looking at that also...i don't know if anything can develop. Alot of shear coming to its face real soon....but, it has a low pressure spin going.
Member Since: September 2, 2007 Posts: 178 Comments: 20443
999. Nolehead
1:39 PM GMT on July 02, 2008
jp, yeah i remember that also...just gotta wait and see...like always.
Member Since: June 3, 2008 Posts: 0 Comments: 1932
998. OUSHAWN
1:38 PM GMT on July 02, 2008
Good morning all!

The GOM still has too much shear and I don't see it letting up anytime soon. However, if I was going to keep an eye out for something interesting to watch out there than it would be right off the upper Texas Coast and around the west and east coasts of Florida...IMO.
Member Since: September 20, 2007 Posts: 0 Comments: 44
997. TampaSpin
1:38 PM GMT on July 02, 2008
993. txalwaysprepared 9:36 AM EDT on July 02, 2008
LOL TS... calm.. for the moment.


watch for those pressure drops....ROFLMAO
Member Since: September 2, 2007 Posts: 178 Comments: 20443
995. Nolehead
1:38 PM GMT on July 02, 2008
kman, that spin is still there jsut west of the islands...still have that same feeling?
Member Since: June 3, 2008 Posts: 0 Comments: 1932
993. txalwaysprepared
1:36 PM GMT on July 02, 2008
LOL TS... calm.. for the moment.
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992. TampaSpin
1:36 PM GMT on July 02, 2008
If i was a betting person i would bet on near miss of North Eastern seaboard
Member Since: September 2, 2007 Posts: 178 Comments: 20443
991. kmanislander
1:35 PM GMT on July 02, 2008
Will BBL
Member Since: August 19, 2006 Posts: 0 Comments: 15842
990. all4hurricanes
1:34 PM GMT on July 02, 2008
I think I'm pretty good in forecasting intensity of hurricanes but where there going baffles me I just go with the cone
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989. kmanislander
1:34 PM GMT on July 02, 2008
Hi MLC / JP

Generally speaking the further North a system spins up at the greater the likelihood it will feel the poleward pull.

The other point of note is that any system forming that far out has a much longer run to the Islands and in the absence of an exceptionally strong high tends not to get beyond 50W.
Member Since: August 19, 2006 Posts: 0 Comments: 15842
988. TampaSpin
1:31 PM GMT on July 02, 2008
983. txalwaysprepared 9:20 AM EDT on July 02, 2008

Hello girl..hows the little hurricanes.....lol
Member Since: September 2, 2007 Posts: 178 Comments: 20443
985. moonlightcowboy
1:20 PM GMT on July 02, 2008
G'morning, K'man! Will this storm feel the poleward pull simply because of its latitude? Would it turn, still, due to that pull if it were further south?
Member Since: July 9, 2006 Posts: 184 Comments: 29610
984. HurrikanEB
1:20 PM GMT on July 02, 2008
Welcome, reedzone
You know what, Boris over there in the pacific looks a litle like Hurricane Vince to me

vince

Boris
Member Since: May 2, 2008 Posts: 12 Comments: 1340
983. txalwaysprepared
1:20 PM GMT on July 02, 2008
Good Morning TS, kman, and everyone.

GOM has lots of rain. We got a nice storm here last night.
And our little invest is looking good this morning.
Member Since: August 18, 2007 Posts: 0 Comments: 1642
982. kmanislander
1:16 PM GMT on July 02, 2008
Good morning all

Both the GFDL and HWRF take 92L NW into the ATL well East of the Islands around 45 West.

That was my thinking last night also.

I have read the various posts about weaker versus stronger systems but from memory a system does not have to become very strong to feel the poleward pull.

In fact, if this reaches TD intensity and then weak tropical storm strength that would be enough to produce a more Northerly track IMO. The real question is timing and if this low has as much going for it as everyone says it does it should become a TD sooner rather than later. That would mean the likelihood of a turn sooner as well unless impeded by a very strong ridge all the way to the islands.

Member Since: August 19, 2006 Posts: 0 Comments: 15842
981. Nolehead
1:14 PM GMT on July 02, 2008
oh i bet so...just glad to see a Florida team doing something for a change....Marlins just bought that 1 year that they were good..lol..hope the Rays don't do the same thing and stay strong!!
Member Since: June 3, 2008 Posts: 0 Comments: 1932
980. Thundercloud01221991
1:14 PM GMT on July 02, 2008
SHIPS has it obtaining cat 2 strength and then weakening it also has sheer increasing at the end of the run
Member Since: August 1, 2006 Posts: 28 Comments: 3716
979. Thundercloud01221991
1:12 PM GMT on July 02, 2008
* ATLANTIC SHIPS INTENSITY FORECAST *
* GOES AND/OR OHC INPUT MISSING *
* INVEST AL922008 07/02/08 12 UTC *

TIME (HR) 0 6 12 18 24 36 48 60 72 84 96 108 120
V (KT) NO LAND 25 27 31 36 41 51 65 73 80 88 87 88 83
V (KT) LAND 25 27 31 36 41 51 65 73 80 88 87 88 83
V (KT) LGE mod 25 26 26 28 30 34 41 49 58 65 70 72 70

SHEAR (KTS) 6 6 5 5 2 1 1 5 1 3 8 16 22
SHEAR DIR 129 121 127 130 161 124 343 24 164 117 263 207 247
SST (C) 27.4 26.7 26.2 25.9 25.9 26.1 26.2 25.7 25.3 25.2 25.5 26.0 26.3
POT. INT. (KT) 129 122 117 115 115 116 116 112 109 109 112 116 118
ADJ. POT. INT. 128 121 116 114 114 114 112 108 107 106 108 109 108
200 MB T (C) -53.6 -52.9 -53.6 -53.8 -53.6 -53.4 -53.7 -53.6 -53.7 -53.1 -53.8 -52.8 -53.0
TH_E DEV (C) 4 4 4 4 4 5 5 5 5 5 5 6 6
700-500 MB RH 78 76 76 76 73 70 64 64 65 64 58 56 54
GFS VTEX (KT) 14 15 17 19 21 21 25 23 21 24 22 25 24
850 MB ENV VOR 78 86 86 95 107 135 156 162 148 131 81 52 17
200 MB DIV 94 131 103 114 97 90 81 90 76 81 32 52 19
LAND (KM) 391 537 661 808 960 1267 1527 1703 1912 2080 2078 2134 2219
LAT (DEG N) 12.0 12.2 12.4 12.5 12.6 12.5 12.3 13.1 14.8 17.3 19.6 22.0 24.1
LONG(DEG W) 20.4 21.8 23.1 24.6 26.1 29.0 31.4 33.2 35.3 37.8 40.6 43.3 45.2
STM SPEED (KT) 11 13 14 15 15 13 10 12 15 17 17 16 13
HEAT CONTENT 9 5 1 0 0 1 2 0 0 0 0 1 4

FORECAST TRACK FROM BAMM INITIAL HEADING/SPEED (DEG/KT):280/ 9 CX,CY: -8/ 2
T-12 MAX WIND: 25 PRESSURE OF STEERING LEVEL (MB): 563 (MEAN=625)
GOES IR BRIGHTNESS TEMP. STD DEV. 100-300 KM RAD: -99.0 (MEAN=20.0)
% GOES IR PIXELS WITH T < -20 C 50-200 KM RAD: -99.0 (MEAN=68.6)

INDIVIDUAL CONTRIBUTIONS TO INTENSITY CHANGE
6 12 18 24 36 48 60 72 84 96 108 120
----------------------------------------------------------
SAMPLE MEAN CHANGE 1. 2. 3. 4. 6. 8. 9. 10. 11. 12. 12. 13.
SST POTENTIAL 0. 0. 0. 1. 3. 7. 11. 15. 19. 21. 23. 24.
VERTICAL SHEAR 1. 2. 4. 6. 9. 12. 14. 16. 17. 17. 16. 14.
PERSISTENCE 0. -1. -1. -1. -1. -1. -1. -1. -1. -1. 0. 0.
200/250 MB TEMP. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0.
THETA_E EXCESS 0. -1. -2. -2. -3. -5. -6. -8. -10. -12. -13. -14.
700-500 MB RH 0. 0. 0. 0. 0. 0. 0. 0. 0. -1. -2. -2.
GFS VORTEX TENDENCY 0. 1. 2. 3. 4. 7. 6. 4. 7. 5. 7. 6.
850 MB ENV VORTICITY 0. 1. 1. 2. 3. 5. 7. 8. 9. 9. 9. 9.
200 MB DIVERGENCE 1. 2. 3. 4. 6. 7. 10. 11. 12. 11. 11. 10.
ZONAL STORM MOTION 0. 0. 0. 1. 1. 1. 1. 1. 1. 2. 2. 2.
STEERING LEVEL PRES 0. 0. 0. 0. 1. 1. 1. 1. 1. 1. 1. 1.
DAYS FROM CLIM. PEAK 0. 0. 0. -1. -1. -2. -2. -2. -3. -3. -3. -4.
----------------------------------------------------------
SUB-TOTAL CHANGE 2. 6. 11. 16. 26. 40. 48. 55. 63. 62. 63. 58.

SATELLITE ADJUSTMENTS ----------------------------------------------------------
MEAN ADJUSTMENT 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0.
GOES IR STD DEV 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0.
GOES IR PIXEL COUNT 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0.
OCEAN HEAT CONTENT 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0.
----------------------------------------------------------
TOTAL ADJUSTMENT 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0.
----------------------------------------------------------
TOTAL CHANGE (KT) 2. 6. 11. 16. 26. 40. 48. 55. 63. 62. 63. 58.

** 2008 ATLANTIC RI INDEX AL922008 INVEST 07/02/08 12 UTC **
( 25 KT OR MORE MAX WIND INCREASE IN NEXT 24 HR)

12 HR PERSISTENCE (KT): 0.0 Range:-45.0 to 30.0 Scaled/Wgted Val: 0.6/ 1.1
850-200 MB SHEAR (KT) : 4.9 Range: 35.1 to 3.2 Scaled/Wgted Val: 0.9/ 1.5
D200 (10**7s-1) : 107.8 Range:-20.0 to 149.0 Scaled/Wgted Val: 0.8/ 1.1
POT = MPI-VMAX (KT) : 93.5 Range: 25.1 to 130.7 Scaled/Wgted Val: 0.6/ 0.7
850-700 MB REL HUM (%): 74.0 Range: 56.0 to 88.0 Scaled/Wgted Val: 0.6/ 0.2
% area w/pixels <-30 C:9999.0 Range: 17.0 to 100.0 Scaled/Wgted Val:999.0/999.0
STD DEV OF IR BR TEMP : 999.9 Range: 35.1 to 3.2 Scaled/Wgted Val:999.0/999.0
Heat content (KJ/cm2) : 3.0 Range: 0.0 to 132.0 Scaled/Wgted Val: 0.0/ 0.0

Prob of RI for 25 kt RI threshold= 999% is 999.0 times the sample mean(12.3%)
Prob of RI for 30 kt RI threshold= 999% is 999.0 times the sample mean( 7.8%)
Prob of RI for 35 kt RI threshold= 999% is 999.0 times the sample mean( 4.5%)
Member Since: August 1, 2006 Posts: 28 Comments: 3716
978. TampaSpin
1:12 PM GMT on July 02, 2008
976. Nolehead 9:10 AM EDT on July 02, 2008

There is so many band wagon jumpers jumping aboard it is amazing.......lol
Member Since: September 2, 2007 Posts: 178 Comments: 20443
977. moonlightcowboy
1:11 PM GMT on July 02, 2008
Good morning, gang! I thought we'd see more consolidation and strengthening through the night. Apparently, that didn't happen. So, it looks like we may have a new ball game, today, as a weaker and slower system should move more westerly with the present steering flow. It's gonna be interesting to see what this one does.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
976. Nolehead
1:10 PM GMT on July 02, 2008
tampa..lol..those Rays are for real, gotta admitt it.
Member Since: June 3, 2008 Posts: 0 Comments: 1932
975. Tazmanian
1:07 PM GMT on July 02, 2008
lol
Member Since: May 21, 2006 Posts: 5091 Comments: 115241
974. Nolehead
1:06 PM GMT on July 02, 2008
morning all...looks to be another intersting day...the GOM sure is firing off!!
Member Since: June 3, 2008 Posts: 0 Comments: 1932
973. stoormfury
1:05 PM GMT on July 02, 2008
the system is moving very slow which will allow the ULL to mve out before it gets to 40w. by that time the ridge would have rebuilt and the ststem will continue west. it is only a matter of time before the models shift southward
Member Since: August 22, 2006 Posts: 0 Comments: 2713
972. TampaSpin
1:03 PM GMT on July 02, 2008
965. NEwxguy 8:55 AM EDT on July 02, 2008

I got a broom for you to borrow if you wanta fly down.
Member Since: September 2, 2007 Posts: 178 Comments: 20443
971. ncforecaster
1:02 PM GMT on July 02, 2008
Hey everyone,

I have to head off to work for a bit, but I didn't want to leave without wishing each and everyone of you a great rest of the day.:)

Most sincerely,
Tony
Member Since: May 17, 2006 Posts: 108 Comments: 1370
970. melwerle
1:00 PM GMT on July 02, 2008
Morning everyone!

Just stopping by - looks a bit interesting...
Member Since: June 28, 2006 Posts: 12 Comments: 1837
968. ncforecaster
12:57 PM GMT on July 02, 2008
Hey Fran,

It is so great to see you posting!:) Thanks so much for the very kind words, and your own contributions to this community are just as much appreciated by myself and all of us here.:) I too hope you have a great rest of the day.:)

Most sincerely,
Tony
Member Since: May 17, 2006 Posts: 108 Comments: 1370
967. hurricane23
12:56 PM GMT on July 02, 2008
Checking in from work...

To me the low pressure area appears to be to the east of the convection right now but all in all i still think this will turn well east of bermuda.

Organization wise this will be a slow but steady process.
Member Since: May 14, 2006 Posts: 8 Comments: 13804
966. TampaSpin
12:55 PM GMT on July 02, 2008
Member Since: September 2, 2007 Posts: 178 Comments: 20443
965. NEwxguy
12:55 PM GMT on July 02, 2008
looking at the water vapor imagery and considering how slow it is moving right now,yesterdays thoughts about it following a weakness,probably won't come to pass,going to be interesting to see how things set up.
Member Since: September 6, 2007 Posts: 881 Comments: 15840
964. FLCrackerGirl
12:49 PM GMT on July 02, 2008
Rob@Crownwx, Excellent Obs.
BIG Pre-Season Thanks For All Your Efforts.
Same Sentiments Too For Nash, Tony, Pat, StormW & Main Board Bloggers!!
You'all Have A WUnderful Day.
Fran
Member Since: August 12, 2004 Posts: 47 Comments: 597
963. ncforecaster
12:49 PM GMT on July 02, 2008
Hey Nash,

Looks like the COC is repositioned SE of the previous one.

Excellent observation!:) This is a perfect example as to why the Global models aren't as reliable as this point of cyclogenesis, as they are when it achieves tropical cyclone intensity (mainly due to proper inialization of the models around a definitive center of circulation).
Member Since: May 17, 2006 Posts: 108 Comments: 1370
962. nrtiwlnvragn
12:48 PM GMT on July 02, 2008
Latest SHIPS text file.

Notice that there are no satellite adjustments since the storm is not in GOES range. Don't know if this would add or subtract to intensity.
Member Since: September 23, 2005 Posts: 14 Comments: 11215
961. ncforecaster
12:41 PM GMT on July 02, 2008
In regards to track forecasts, it is simply too early to make a definitive forecast at this point in time, for the Global models have a more difficult time with systems that are still in the process of cyclogenesis as opposed to one that has achieved tropical cyclone intensity. It is all about "persistance" for the development of this system, and "patience" for those who are tracking it.:)
Member Since: May 17, 2006 Posts: 108 Comments: 1370
960. nash28
12:40 PM GMT on July 02, 2008
For now, the models are overdoing it a bit on itensity in the short term.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
959. watchingnva
12:39 PM GMT on July 02, 2008
all i know os as long as 92l takes its sweet time getting organized and stronger....the more westward its going to go...if it stays like it is for the next 24-48 hours, i have a feeling those models will start doing a southerly shift. we will have to see what happens.
Member Since: September 7, 2005 Posts: 7 Comments: 1516
958. nash28
12:38 PM GMT on July 02, 2008
Looks like the COC is repositioned SE of the previous one.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
957. nrtiwlnvragn
12:37 PM GMT on July 02, 2008
...INITIAL CONDITIONS...
LATCUR = 12.0N LONCUR = 20.4W DIRCUR = 280DEG SPDCUR = 9KT
LATM12 = 11.7N LONM12 = 18.6W DIRM12 = 280DEG SPDM12 = 9KT
LATM24 = 11.4N LONM24 = 16.5W
WNDCUR = 25KT RMAXWD = 60NM WNDM12 = 25KT
CENPRS = 1009MB OUTPRS = 1012MB OUTRAD = 120NM SDEPTH = M
RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM


Link
Member Since: September 23, 2005 Posts: 14 Comments: 11215
956. 69Viking
12:35 PM GMT on July 02, 2008
Good morning all! I see we have a wave still "plowing westward" as TWC would say. JP you're killing me, too funny this morning you are!
Member Since: August 25, 2006 Posts: 1 Comments: 3055
955. nash28
12:35 PM GMT on July 02, 2008
Good morning Allan. Welcome.

SFC low still looking good. We will most likely have TD2 at some point today.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
954. reedzone
12:31 PM GMT on July 02, 2008
Hey, my name is Allan, I've been reading this blog since 2006.. Anyways, havent seen an update image of 92L, the way it was going last night, I thought we'd have a TD on our hands this morning but mother nature has other plans :)
Member Since: July 1, 2008 Posts: 13 Comments: 7396

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

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