Atlantic Sea Surface Temperatures and Anomalies

['CaneFreak]

While we are waiting for activity in the basin to pick up, clearly the western Atlantic is beginning to warm up substantially.

[cycloneye]

Look how the Caribbean look as of August 7 with this very warm TCHP.

[gatorcane]

Waters off Africa in the Indian Ocean are still relatively cool (top graphic) but look how they are starting to warm up (bottom graphic) when you look at the 5-day SST change. Maybe this will allow more waves and disturbances to generate over Africa?

Notice also SSTs across the Caribbean are still warming:

['CaneFreak]

Good catch. This will definitely be something to watch for in the coming days.

[TropicalAnalystwx13]

Waters off Africa in the Indian Ocean are still relatively cool (top graphic) but look how they are starting to warm up (bottom graphic) when you look at the 5-day SST change. Maybe this will allow more waves and disturbances to generate over Africa?

Notice also SSTs across the Caribbean are still warming:

http://img823.imageshack.us/img823/5260/8m2.gif

Warming waters in the Indian Ocean are a bad sign. The Indian Ocean Dipole is currently negative, meaning cooler waters. This enhances the African monsoon and puts the atmosphere in a La Nina-like state. During a positive IOD, when the waters are warm, the monsoon is weakened. The upper-level axis of the subtropical ridge is shunted farther south than normal as well, creating a lid for convective activity => less vertical instability. This was the problem in 2007 and 2011.

['CaneFreak]

Yes but don't you need tropical waves to go over warmer than normal waters in order for them to grow BEFORE going over the African continent? It sure seems that if they went over cooler than normal waters, they would be less potent tropical waves and they might die before they could even get to the AEJ. I think I know what you are saying in an overall sense though.

Warming waters in the Indian Ocean are a bad sign. The Indian Ocean Dipole is currently negative, meaning cooler waters. This enhances the African monsoon and puts the atmosphere in a La Nina-like state. During a positive IOD, when the waters are warm, the monsoon is weakened. The upper-level axis of the subtropical ridge is shunted farther south than normal as well, creating a lid for convective activity => less vertical instability. This was the problem in 2007 and 2011.

[Kingarabian]

Yes but don't you need tropical waves to go over warmer than normal waters in order for them to grow BEFORE going over the African continent? It sure seems that if they went over cooler than normal waters, they would be less potent tropical waves and they might die before they could even get to the AEJ. I think I know what you are saying in an overall sense though.

Warming waters in the Indian Ocean are a bad sign. The Indian Ocean Dipole is currently negative, meaning cooler waters. This enhances the African monsoon and puts the atmosphere in a La Nina-like state. During a positive IOD, when the waters are warm, the monsoon is weakened. The upper-level axis of the subtropical ridge is shunted farther south than normal as well, creating a lid for convective activity => less vertical instability. This was the problem in 2007 and 2011.

You need a balance, really.

[TropicalAnalystwx13]

Yes but don't you need tropical waves to go over warmer than normal waters in order for them to grow BEFORE going over the African continent? It sure seems that if they went over cooler than normal waters, they would be less potent tropical waves and they might die before they could even get to the AEJ. I think I know what you are saying in an overall sense though.

Warming waters in the Indian Ocean are a bad sign. The Indian Ocean Dipole is currently negative, meaning cooler waters. This enhances the African monsoon and puts the atmosphere in a La Nina-like state. During a positive IOD, when the waters are warm, the monsoon is weakened. The upper-level axis of the subtropical ridge is shunted farther south than normal as well, creating a lid for convective activity => less vertical instability. This was the problem in 2007 and 2011.

Tropical waves form over East Africa as a result of instability created by the Sahara Desert and the Guinean Forest. The potency of the waves depend on the amount of instability, which depends on the difference in moisture and temperature between the two aforementioned locations. That's why a cool Gulf of Guinea is favorable as well...it creates a higher difference in temperature => higher instability. During a positive IOD, we get enhanced convection over the Indian Ocean. Rising air here means it's sinking over Africa. Sinking air over Africa => less waves => more dry air in the East Atlantic.

[TropicalAnalystwx13]

This is a composite of the sea surface temperatures observed across the Indian Ocean during the top 10 ACE hurricane seasons (2005, 1950, 1995, 2004, 1961, 1955, 1998, 1999, 2003, 1964). Note the overwhelmingly cool signature:



Excerpt from The 2011 North Atlantic Hurricane Season: A Climate Perspective:

"Historically, there have been eight significant positive IOD events since reliable global
OLR data became available in 1979. While these
events have occurred during all phases of ENSO,
they are typically associated with reduced Atlantic
hurricane activity..."

[CrazyC83]

Notice the SST's in the Atlantic rising fast...perhaps the lack of activity is warming the water up? Who knows.

[gatorcane]

SSTs around Florida, especially in the Straits of Florida are quite warm but are noticeably cooler and below normal in the Southeastern GOM area:

[Ntxw]

Tropical waves form over East Africa as a result of instability created by the Sahara Desert and the Guinean Forest. The potency of the waves depend on the amount of instability, which depends on the difference in moisture and temperature between the two aforementioned locations. That's why a cool Gulf of Guinea is favorable as well...it creates a higher difference in temperature => higher instability. During a positive IOD, we get enhanced convection over the Indian Ocean. Rising air here means it's sinking over Africa. Sinking air over Africa => less waves => more dry air in the East Atlantic.

This is interesting. I wonder why it conflicts with the research that states there is a strong correlation between convection firing in the IO (MJO related phases 2-3) and significantly increasing Atlantic activity. The IO monsoon plays an important role in feeding the ITCZ through Africa thus increasing moisture downstream over the Atlantic (rise in Instability). Sinking air over Africa itself is better correlated with convection near the Maritimes and definitely the WPAC, I'm not familiar with the IOD though so I'm uncertain if it's a whole different ballgame but it just seems to conflict.

[TheStormExpert]

Are the SST's really in the 60F range in SE Gulf or am I just seeing things?

[hurricanetrack]

TheStormExpert: Guessing those are just clouds that the sat cannot see through too well and so it shows up as bad data or in this case, cold bleeping water.

[Alyono]

2005 also had one of the weakest CV seasons of the past couple of decades, really only behind 1997. Only had 1 storm forming south of 20N east of 40W, that being Irene.

It also had early season activity east of the islands.

[psyclone]

I'm throwing a flag on the Florida sea surface temp graphic posted above...there's certainly corrupt data for those gulf temps...the only way you get temps in the 60's is a brief instance where someone dumped their beer cooler. uniformly warm temps are the rule this time of year. I can attest to the bath water depicted around the tampa bay area... our beaches feature temps in the upper 80's to near 90...typical for August.

[TropicalAnalystwx13]

Tropical waves form over East Africa as a result of instability created by the Sahara Desert and the Guinean Forest. The potency of the waves depend on the amount of instability, which depends on the difference in moisture and temperature between the two aforementioned locations. That's why a cool Gulf of Guinea is favorable as well...it creates a higher difference in temperature => higher instability. During a positive IOD, we get enhanced convection over the Indian Ocean. Rising air here means it's sinking over Africa. Sinking air over Africa => less waves => more dry air in the East Atlantic.

This is interesting. I wonder why it conflicts with the research that states there is a strong correlation between convection firing in the IO (MJO related phases 2-3) and significantly increasing Atlantic activity. The IO monsoon plays an important role in feeding the ITCZ through Africa thus increasing moisture downstream over the Atlantic (rise in Instability). Sinking air over Africa itself is better correlated with convection near the Maritimes and definitely the WPAC, I'm not familiar with the IOD though so I'm uncertain if it's a whole different ballgame but it just seems to conflict.

The MJO still has a profound positive influence over Africa during octants 2/3. It's not really until 4-5 when it starts to become unfavorable.

[jordanwx]

Yes but don't you need tropical waves to go over warmer than normal waters in order for them to grow BEFORE going over the African continent? It sure seems that if they went over cooler than normal waters, they would be less potent tropical waves and they might die before they could even get to the AEJ. I think I know what you are saying in an overall sense though.

Warming waters in the Indian Ocean are a bad sign. The Indian Ocean Dipole is currently negative, meaning cooler waters. This enhances the African monsoon and puts the atmosphere in a La Nina-like state. During a positive IOD, when the waters are warm, the monsoon is weakened. The upper-level axis of the subtropical ridge is shunted farther south than normal as well, creating a lid for convective activity => less vertical instability. This was the problem in 2007 and 2011.

As TropicalAnalyst already said, these waves feed off baroclinic instability. In other words, they require a density (pressure) gradient (which is created by temperature and moisture gradients). Thus, the cooler the Indian Ocean is, the higher pressures will be over the Indian ocean, creating a stronger gradient. The cooler the Indian Ocean is the less moisture it will have as well. Less moisture means less rising air (higher surface pressures), and again we see the pressure gradient is enhanced between the Saharan heat low and the relatively higher pressures over the Indian Ocean.

So the cooler the Indian Ocean (-IOD), the more baroclinic energy the waves will have to feed off. This is no different than how we like to see the Gulf of Guinea cooler than normal. Furthermore, while it would appear logical to think waves will have more moisture available to them when the Indian ocean is warm, that is not entirely true. When the ocean is warmer, more air rises over the ocean, reducing the sea-breeze effect. As a result, less moisture is advected across the continent to the Sahel region (where waves form).

[Ntxw]

The MJO still has a profound positive influence over Africa during octants 2/3. It's not really until 4-5 when it starts to become unfavorable.

Correct, which is why in my post I stated Maritime Continent is when Africa starts getting dry (phases 4-5) not the Indian Ocean phases (2+3) conflicting with the idea of IO convection (rising air) creating subsidence in Africa that you mentioned in the previous post.

[jordanwx]

The MJO still has a profound positive influence over Africa during octants 2/3. It's not really until 4-5 when it starts to become unfavorable.

Correct, which is why in my post I stated Maritime Continent is when Africa starts getting dry (phases 4-5) not the Indian Ocean phases (2+3) conflicting with the idea of IO convection (rising air) creating subsidence in Africa that you mentioned in the previous post.

There's a difference. When the MJO is in phases 2 and 3, you still have rising air over the African continent. When the IOD is positive (or just the Indian ocean is warm as a whole), you favor less convection over the African continent.