Hurricane warnings for Baja; 94L forming spiral bands

By: Dr. Jeff Masters , 3:36 PM GMT on August 31, 2009

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Hurricane warnings are in effect for the southern tip of Mexico's Baja Peninsula, where powerful Hurricane Jimena is expected to make landfall Tuesday night or Wednesday morning. The hurricane is in an environment with low wind shear, 5 - 10 knots, and warm Sea Surface Temperatures (SSTs), 30°C. Shear is expected to remain low, and SSTs will decline to 28°C with a corresponding decrease in total oceanic heat content between now and landfall, and these conditions should mean that Jimena will be a Category 3 or 4 hurricane at landfall. Outer rain-bands of the hurricane will be appearing on Los Cabos radar soon, though the Mexican Weather Service web site has been hard to reach today. The computer models are split, with one camp calling for a landfall in southern Baja, and the other camp calling for landfall farther north near central Baja. The official NHC forecast splits the difference between these two solutions, and landfall could occur anywhere along a long stretch of the Baja coast. At this point, the UKMET model's solution taking Jimena westward out to sea is being discounted, since it is an outlier.

After Jimena makes initial landfall on Baja, it will cross over the Gulf of California and make landfall on Mainland Mexico. Depending upon how up along the coast this second landfall occurs, Arizona may receive moisture from Jimena late this week that will be capable of causing flooding rains.


Figure 1. Image of Hurricane Jimena taken by NASA'a MODIS instrument at 2020 UTC Sunday, 8/30/09.

Invest 94L
The well-organized tropical wave (94L) near 14.5N, 52W, about 500 miles east of the central Lesser Antilles Islands, continues to be a threat to develop into a tropical depression. Visible satellite imagery and this morning's QuikSCAT pass do not show a surface circulation yet, though 94L does have a large envelope of moisture and some modest heavy thunderstorm activity. QuikSCAT noted winds up to 30 mph. Water vapor satellite loops show that 94L has moistened the region surrounding it considerably, and dry air from the Saharan Air Layer is not a major impediment to development. Wind shear is a low 5 - 10 knots, and the ocean temperature are a moderately warm 28°C. Visible satellite loops over the past two hours show low-level spiral bands developing on 94L's northeast side, and I give a 70% chance the Hurricane Hunters will find a tropical depression or tropical storm on Tuesday when they investigate 94L.


Figure 2. Morning satellite image of 94L, showing low-level spiral bands developing on the northeast side.

The center of 94L probably passed over Buoy 41040, located at 14.5N, 53W over the past hour. Winds blew northeasterly early this morning, then went calm, then shifted to southerly late this morning. The winds were less than 10 knots during the center passage, so the circulation of 94L is not yet well-defined. The pressure fell significantly as 94L moved over the buoy (seen only after one removes the wiggles due to daily atmospheric tide effect present in the tropics). 94L will appear on Martinique radar on Tuesday.

The forecast for 94L
Shear will remain low, 5 -10 knots, over the next 5 days, SSTs will be warm, in the 28 - 29°C range, and dry air should have only a minor inhibiting effect, so I can't see anything that will prevent 94L from developing into a tropical depression over the next 1 - 2 days. The HWRF model develops 94L into a hurricane 4 days from now, as does the SHIPS intensity model, but other models, such as the GFDL, ECMWF, and GFS, do not develop 94L at all.

Model solutions for the track of 94L are divergent. Water vapor satellite loops show two upper-level lows to the north and northwest of 94L that are pulling the storm to the west-northwest, and 94L's motion is expected to range between the west-northwest and northwest over the next three days. By Tuesday, 94L will slow down from its current 15 mph forward speed to about 10 mph. Most of the models predict that the steering influence of the upper-level lows will pull 94L far enough north that the storm will miss the Lesser Antilles, with a closest approach occurring Wednesday and Thursday. However, the ECMWF and HWRF models have 94L passing within 200 miles of the islands, and the northern Lesser Antilles may experience tropical storm conditions on Thursday.

At the longer ranges, the fate of 94L is highly uncertain. The Canadian model turns 94L to the north near Bermuda, then out to sea, while the NOGAPS model foresees a threat to the U.S. East Coast early next week. Both of these solutions are believable. The Hurricane Hunters are scheduled to make their first flight into 94L on Tuesday afternoon at 2pm EDT.

Elsewhere in the Atlantic
The remains of an old cold front are bringing cloudiness and showers to the northern Gulf of Mexico and waters offshore North and South Carolina. The GFS and NAM models indicate an area of low pressure may develop along this old front near the Florida Panhandle or off the coast of North Carolina by Thursday. However, such a low may be extratropical and not tropical.

My next post will be between 3 - 5pm this afternoon.

Jeff Masters

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Afternoon everyone! Convection is holding for 94L and a TD if not Erika is possible tomorrow when the Hurricane Hunters go out there. An anticyclone is still over the invest so development looks good with great outflow. All of the USA coastline from Texas to Maine needs to just watch 94L for now. Chances are becoming more better for a High Pressure to build in and steer it west, not a certainty just yet. Give it a few more days and we should have an idea of where it will be going.
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Hurricane Preparation Entry
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I would think if it slows down to 10mph, and putting it possibly near the Northern Lesser Antilles around Thursday, it could be the weekend before we get a good handle on which way it will go.
Member Since: September 5, 2007 Posts: 0 Comments: 3488
The Miami NWS discussion mentions the activity east of the Bahamas as an inverted trough which will be absorbed into the front in northern Fla and shunted up to NC. No mention of tropical development on that area. 94L is of more concern if the ridge builds into Florida late next week as forecast. Just when you were starting to feel good about the number of troughs off the southeast coast....
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Quoting weathermanwannabe:


Thanks; so basically, if I read the chart correctly, that 30-40 knot sheer area will "step aisde" as the system moves onward...If that it indeed the case, then we should expect a TD/Storm by tommorow and, then, the models can get a better handle on the future track.


Not exactly, it will move with the anti-cyclone. Look at the thin lines on the map with the arrows. That shows the direction of the shear. The anti-cyclone right on top of the system is pretty easy to see. Those thin lines are the actual wind direction of the shear. Stregth of the shear is the yellow lines.
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Quoting ncstorm:
good afternon everyone!

What's the difference between an extratropical and a tropical storm and are extratropical storms named?


Extratropical storms exist at mid latitudes, i.e. outside of the tropics.
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46. amd
looks like I need to make sure I have the crow recipes ready... I was one of those who thought shear was going to seriously affect 94L, but 94L continues to improve in organization throughout the morning. And, the anticyclone protecting 94L is becoming better defined.

It should only be a few more hours before the LLC and MLC become co-located with each other. When that happens, they can declare 94L either a TD or even TS Erika at any time.
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Quoting TheCaneWhisperer:


Only some were saying it but, Dr. Masters could be wrong as well. Only time will tell.


That 30 knots IS the anticyclone. Done mentioning it. If the L moves out from under that, then yes, shear looks like it would be a problem.

Look at the "thin" lines and arrows.

Link

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It looks like a lot is popping up in the tropics....

Any thoughts on the area above the Caribbean? What about the wave just off of Africa? GOM?
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Good afternoonish...
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Of note 12z GFS finally on board with some development just north of the islands.
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Quoting Seastep:


The anti-cyclone. If you look, it is precisely the anti-cyclone creating the shear and that shear should move out ahead of the L as long as the anti-cyclone follows along.


Thanks; so basically, if I read the chart correctly, that 30-40 knot sheer area will "step aisde" as the system moves onward...If that it indeed the case, then we should expect a TD/Storm by tommorow and, then, the models can get a better handle on the future track.
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I think we all need to keep at least one eye on this thing untill they get a better handle on 94L.... Remember the High will build back in and could very well move it back to the west.... Just to soon to say what will happen....

Taco :0)
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36. IKE
Quoting weathermanwannabe:


Hey Ike...Forget the "blog" experts; the radar derived CIMSS information is wrong?


What I see is an invest that has a high-pressure system near to where the COC is at. Yesterday I wondered too about the excessive shear that is west and north of 94L. Others on here(yesterday), were saying the high and 94L would move in tandem.

Now Dr. Masters and Accuweather both say the same...that shear will remain low for the next several days. I'll take them at their words. They have a lot more knowledge then I do concerning the tropics.
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Quoting BrockBerlin:
I believe the presence of an anticyclone might explain the low shear forecast, but I did not believe the anticyclone was directly over 94L.


Looks right overhead to me.

Link
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No, extratropical storms are not named. They are run-of-the-mill low pressure areas.
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Well, back to work. You guys and gals try to get it all figured out by the time I get back, ok? Thanks. Knew I could count on ya'll.
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Jimena Multiplatform Tropical Cyclone Kinetic Energy and Intensity 1200 UTC


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451 that was a good post, system has and still does have elongated center of circulation. Maybe two centers this I think is holding back development.
Member Since: August 18, 2008 Posts: 0 Comments: 3113
Yeah, the CIMSS shear map showed 30kt of shear directly infront of 94L
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Quoting caneluver:
5-10 knots of shear for the next 5 days!!!!!!!! What's up with all these blog experts saying 30 to 40 knots?


Only some were saying it but, Dr. Masters could be wrong as well. Only time will tell.
Quoting BrockBerlin:
I believe the presence of an anticyclone might explain the low shear forecast, but I did not believe the anticyclone was directly over 94L.


Your right, the anticyclone acts like a shield or bubble from the shear, yes shear is high to the North of 94L but as long as that Anticyclone is nearby the shear won't do much to it, now if that Anticyclone were to weaken or really become displaced from 94l then yes shear would hurt it.
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good afternon everyone!

What's the difference between an extratropical and a tropical storm and are extratropical storms named?
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As we've seen all year, the shear forecasting is terrible. Several storms have experienced much more shear than than forecast was calling for...
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Quoting weathermanwannabe:


Hey Ike...Forget the "blog" experts; the radar derived CIMSS information is wrong?


The anti-cyclone. If you look, it is precisely the anti-cyclone creating the shear and that shear should move out ahead of the L as long as the anti-cyclone follows along.
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Jimena Latest Image 1415 UTC



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Quoting hurricanehanna:
Thanks Doc. Okay, so we sit, and wait and watch....I hate that part.


Good one! lol
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Thanks Doc. Okay, so we sit, and wait and watch....I hate that part.
Member Since: September 5, 2007 Posts: 0 Comments: 3488
Latest SAL Split Window,combo
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Quoting IKE:


Easy to answer....their wrong!


I wonder if part of the reason is distance on these maps is deceiving, and is the shear moving along with the wave?
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My comment was to 451. Good Post.
Member Since: July 17, 2009 Posts: 71 Comments: 26949
Quoting IKE:


Easy to answer....their wrong!


Hey Ike...Forget the "blog" experts; the radar derived CIMSS information is wrong?
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I want to repost a couple of things because I think it's of value to anyone who doesn't see the older blog. Alright, speculate away what this means in term of a COC

Now that is a post!!!
Member Since: July 17, 2009 Posts: 71 Comments: 26949
LOL...@ IKE
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12. IKE
Quoting caneluver:
5-10 knots of shear for the next 5 days!!!!!!!! What's up with all these blog experts saying 30 to 40 knots?


Easy to answer....their wrong!
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Thanks Dr....Having a little bit of trouble understanding the "Shear will remain low, 5 -10 knots, over the next 5 days" when the current CIMSS charts show a pocket of 30-40 knots near/around the NE quadrant right now..If your solution is correct, and sheers does in fact remain low for right now, then I would prefer rapid development in the short term, and a miss to the North of the Islands, to better the chances of a fish rather than later in the forecast period where things could become problematic for the Bahamas/SE Coast if sheer prevents significant development until after it is North of the Leewards.
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i think 94L will develope into a storm of hurricane by tommorow night.
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Glad you're back with a comprehensive update doc!

To any and all>>>>The forecast for 94L
Shear will remain low, 5 -10 knots, over the next 5 days
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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.