SEVERE WEATHER OUTLOOK…ATLANTIC HURRICANE SEASONAL FORECAST…TROPICAL DISCUSSION…MAY 11, 2012…ISSUED 12:05 P.M. EDT

SPECIAL UPDATE: SPECIAL TROPICAL WEATHER OUTLOOK ISSUED BY THE NHC IN MIAMI AT 1:40 P.M. EDT.

A Non Tropical Low pressure center was designated INVEST 92L early this afternoon.  Based on the most recent satellite loop imagery, the low was near Lat. 34.0N;Long. 30.8W.  The low is quasi-stationary at the moment.  Based on model guidance, and mainly the current forecast steering layers maps from the PSU e-WALL site, I expect this low to complete a cyclonic loop over the next 24 hours, and eventually be steered off toward the NE.  Maximum sustained winds were estimated to be 50 mph.

GLOBAL TRACKS 7 92L TRACKING MAP

Based on earlier satellite loop imagery, 92L did have some ample convection wrapped near the center, albeit recent imagery shows the convection has waned quite a bit.  You may be asking yourself, WHAT?  The reason this low was able to fire convection, even though the sst’s are only around 66-68F, is due to the cold core nature in the mid to upper levels of the atmosphere.  The difference in the warmer ocean water, in relation to the upper and mid levels of the atmosphere, induced a steep enough lapse rate to develop convection.

INVEST 92L FLOATER SATELLITE LOOP IMAGERY


Once this system completes its loop, it MAY develop convection for a short time, and based on the current wind shear forecast, wind shear is forecast to remain at or just below the current 15-20 kts.  This could allow the system to briefly acquire sub-tropical characteristics. Based on the STWO from the hurricane center, this system at this time has a MEDIUM (40%) chance for development…however I do feel chances may be slimmer than 40% within the next 24-36 hours.

NHC GRAPHIC TROPICAL WEATHER OUTLOOK

I will continue to monitor this system, mainly for practice, over the next few days.

SEVERE WEATHER RISK: TSTMS
FIRE WEATHER RISK: NONE
TROPICAL STORM FORMATION: MEDIUM (40%)
COASTAL STORM DEVELOPMENT: LOW

Good afternoon!

The Storm Prediction Center does not indicate any Severe Thunderstorm threat today.

SPC DAY 1 CONVECTIVE OUTLOOK

Based on sounding analysis, and information based in the outlook, there is a possibility for an upgrade to a SLIGHT risk of Severe Thunderstorms, which would most likely occur over east and east central Texas.  The Sounding from BRO indicated the highest prob for both hail and tornadic activity.

NWS WATCH, WARNING and ADVISORY DISPLAY 

INTELLICAST DOPPLER RADAR and INTERACTIVE RADAR LINK 

http://www.intellicast.com/Local/WxMap.aspx?location=USLA0338&weather=hdRadarSmoothPaletteA 

In the Tropical world, the GFS model still indicates tropical development around the 21-23 May time frame.  It has backed off hurricane strength on the entity, and now shows a weak Tropical Storm in the W. Caribbean around that time.  The GFS has been fairly consistent now in developing a low, however this could be attributed to convective feedback issues with the GFS, and with the GFS predicting a strong upward motion pulse from the MJO to enter the Caribbean.  This will remain to be seen, as the ECMWF shows a weaker pulse, and brings it into Octants 5 & 6 (near Asia), with the GFS being more aggressive, and placing it within Octant 8.  For those not familiar with this jargon, or the MJO Index, we here on the Atlantic side usually see some type of development when the MJO has a moderate to strong pulse in Octants 8 and 1 and sometimes when traversing into Octant 2. The further the line is away from the center circle, the stronger the pulse.

MJO INDEX

Based on analysis of the only 2 medium to long range models (GFS;ECMWF), albeit I’m looking for more consistency in the ECMWF, There could be early season development.  The GFS is more aggressive, showing a T.S., and the ECMWF in the current run shows a 1008 mb closed isobar in the same location.  One parameter that seems to support this is, the 500 mb Mean Anomaly, and the 500 mb Mean Anomaly Departure maps indicate the lowering of pressure heights in the W. Caribbean/extreme SW GOMEX around the 23rd of the month.

GFS MODEL OUTPUT

ECMWF MODEL OUTPUT

Analysis of the latest run of the 850-200 mb shear forecast map (GFS) indicates an upper level anticyclone may try to migrate from the EPAC into the W. Caribbean with a reduction in wind shear.

The 8-10 day 500 mb mean chart shows 500 mb trofing entering close to the W. Caribbean.  If you notice, the red and orange anomalies over the Great Lakes area would support the idea of lowering pressures in the GOMEX/Caribbean area.

8-10 DAY 500 MB MEAN

TCHP (Tropical Cyclone Heat Potential) is once again on the increase, but still slightly behind last years values at this time.

TCHP MAY 10, 2012

TCHP MAY 10, 2011

The SOI (Southern Oscillation Index) continues in the positive.  As long as this remains positive, it will delay the onset of El Nino


At any rate, I will continue to monitor this situation for any development.

2012 ATLANTIC HURRICANE SEASONAL FORECAST:

June 01 marks the start of the Atlantic Hurricane Season.  After analysis of current and forecast indices and parameters, my seasonal outlook is as follows:

Total Named Storms: 11-12
Total Hurricanes: 5-6
Total Intense Hurricanes: 2-3

The outlook is based on a few factors that can or should reduce storm activity.

1.)  Most of the Global Model data indicate El Nino conditions during the last half of the Summer.  This has the tendency to increase vertical wind shear across the Caribbean and portions of the Atlantic MDR.  However, it is the opinion of this forecaster that El Nino may not come on as strong as forecast, or may experience a short delay in the onset.  My basis on this is, over the past week or so, the SOI has climbed back into the positive side of the index, which indicates higher than normal pressures over Tahiti, and lower than normal pressures over Darwin, Australia.  This leads to trade winds blowing stronger from east to west in the Equatorial Pacific, which has slowed warming of the SST’s for now.  Once and if we have the onset of El Nino, then we have to account for the “lag” time of the atmosphere to fully respond.  This may allow for El Nino to not be too detrimental in allowing a below average season.  My thoughts are still with a Neutral state with a warm bias.

2.) Given the positive NAO we have been in, the E. ATL and most of the Caribbean have displayed cooler than normal sst anomalies.  This should have a negating factor on the upcoming Cape Verde season.  IF the NAO stays positive, I do not look for waters in the E. ATL to warm anymore, and look for above average wind shear.  Should the NAO come down to neutral to negative, waters may warm slightly.  

3.) SAL:  The Saharan Air Layer has been active due to the increased trade winds, which blocks sunlight from reaching the ocean, thus aiding in keeping the EATL cooler.  However, the SAL has not been as strong as some past events.  Right now, it will be hard to say if the SAL will be very active this summer, as cooling in the Gulf of Guinea has allowed for the ITCZ, or Monsoon Trof to lift northward over a portion of the Sahel region, which should allow for some increased rainfall.  This is one unknown variable right now.

4.)  GOMEX SST and GULFSTREAM TEMP:  The GOMEX and Gulfstream are displaying warmer then normal sst anomalies…this would tend to be an enhancing factor for any systems forming or moving into these areas.  However, this would occur nearer to the start and end of the season.

5.) TCHP:  Tropical Cyclone Heat Potential (or lack of) is another slightly negating factor, however I use this mainly for Intense Hurricane factors, and possible Rapid Intensification factors.  The TCHP overall is below the level of what we had this time last season. However, TCHP has been known to ramp up quite quickly in the Caribbean if trade winds relax.

On a side note, given the uncertainty of the forecast El Nino, state of the NAO in the long range, some parameters may change.

So, in short, my totals are based on the newer long term average (11-6-2) and the analog years of 2001, 2006 and 2009, based on the ONI (Oceanic Nino Index) and averaging these 3 factors.  That average is then added to the total I come up with by adding and subtracting the various positive and negative factors in a formula I worked up.  This total (Analog avg total) and my total, working with the normal avg and my factors, are added and divided by 2.  Then the analogs are reviewed again, and my totals are weighted against these and the long term average to come up with a “normalized” range.  I am looking for the GOMEX to be active with mainly “home brew”, albeit should a system make it up from the Caribbean, watch for possible rapid intensification.  Same holds true for anything crossing the Gulfstream, albeit a shorter time over the warmer temps.  Given the cooler EATL temps., I am not looking for a busy Cape Verde season.  It would appear any tropical waves crossing the ATL will need to get past 40W as we have seen in some seasons, before any development takes place, so development this year will most likely take place in the Gulf and outside of the MDR.  Again, this could change slightly with the addition of anymore of the variables becoming positive.

Have a fantastic Friday!

T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST/TROPICAL FORECASTER
MEMBER WEST CENTRAL FL AMS
CERTIFIED SKYWARN OFFICIAL STORM SPOTTER (advanced)

About these ads

About palmharborforecastcenter

I am a Tropical Forecast meteorologist, providing hurricane forecasts during the Atlantic Hurricane Season. I retired from the U.S. Coast Guard in July of 2001. Meteorology became my passion in high school, and I have continued my educational background in meteorology since 1996, when I undertook the study of Tropical Meteorology. While working toward my degree, I had to unexpectedly withdraw from college due to my oldest sons medical reasons. I do however, meet the educational criteria of the AMS to be recognized as a meteorologist. Studies include, but are not limited to the Navy Aerographers Mate course, Naval METOC meteorology course, Meteorology 2010 Sophomore level course while attending St. Petersburg College, Clearwater, FL., Basic Forecasting course for operational meteorologists from Rapid WX, meteorology institute, a four month meteorological internship, and extensive research on numerous meteorological topics such as the MJO, NAO, satellite imagery interpretation, etc. I have been forecasting Tropical Weather (Tropical Storms and Hurricanes) since 1996, with my main client being three different Coast Guard Commands.
This entry was posted in Severe Weather, Tropical Synopsis. Bookmark the permalink.

13 Responses to SEVERE WEATHER OUTLOOK…ATLANTIC HURRICANE SEASONAL FORECAST…TROPICAL DISCUSSION…MAY 11, 2012…ISSUED 12:05 P.M. EDT

  1. Mike Doll says:

    Thanks Storm Appreciate the forecast and the Outlook. Look forward to reading and hopefully learning from your Tropical forecast this season

  2. heyengineer says:

    Much thanks for the forecasts and explanations Storm. You rock!

  3. stefanie says:

    Thanks for the updates Storm. :)

  4. originallt says:

    Thanks for updating the situation Storm, and making clear what will happen.

  5. originallt says:

    The NHC seems to be giving this feature, 92L, a 40% chance of developing. BUT it appears to be moving Eastward, towards Europe, so it should not bother us.

  6. originallt says:

    92L in the eastern Atlantic? Wow, that’s early.

  7. Thanks Storm. I’ll be curious if the GFS will hold true to the Caribbean system. Thanks for your forecasts…it’s good to see you back in Hurricane mode!! Have a great day everyone!!

  8. stefanie says:

    Thanks Storm. I understood every word of that except the math. Lol. I think we’ve been put under a slight risk for today. I apparently slept through our rain last night. Sun shining brightly right now. I don’t know what will happen in the tropics this year but if Texas can get her rains without a natural disaster on the coast somewhere the storms can stay away from here again! Enjoy your weekend! :)

  9. originallt says:

    Thanks Storm, good to see a quiet weather pattern for awhile, although Dellamom’s area looks to get very wet!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s