SEVERE WEATHER THREAT: MODERATE
TROPICAL STORM FORMATION: CLAUDETTE
ALL forecasts contained on this site, are based on my analysis and knowledge of various forecast tools, including information contained in NHC products, and are not copies from any other entity.
*NOTE: In the TROPICAL STORM FORMATION line above, probabilities are for during the next 5 day period. My personal probability will be listed as either NONE, MONITORING or PROBABLE. This does not necessarily mean something will develop, but that certain forecast conditions are likely to be present, favoring development. Once NHC products become available, then the appropriate probability and percentage will be used.
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Current Storm Total for 2015:
TOTAL STORMS: 3
INTENSE HURRICANES: 0
U.S. LANDFALLS: 2
StormW Seasonal Forecast:
TOTAL STORMS: 8 – 10
HURRICANES: 3 – 5
INTENSE HURRICANES: 1 – 2
Good day everyone!
Well, if you’re like me, you’re at this point wondering WTH? I know I am. Tropical Storm Claudette came as a surprise to most of us, in the tropical weather community, or at least me, as forecast conditions did not indicate conditions favorable for a transition to Tropical Status of INVEST 92L. In fact, I had a little time before work, and took a look at the NHC Tropical Weather Outlook. Early this morning, the NHC had downgraded the probability of Tropical Cyclone formation over the next 5 days to 10%. However, while I was at work today, early this afternoon, the NHC indicated that convection had increased and persisted long enough, and that 92L had lost all frontal characteristics, so at 1:00 p.m. AST, the NHC issued this SPECIAL DISCUSSION:
TROPICAL STORM CLAUDETTE SPECIAL DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL
AL032015 100 PM AST
MON JUL 13 2015
The small low pressure area that moved off the coast of North Carolina over the weekend has lost its frontal characteristics and acquired organized deep convection overnight. The convection, albeit primarily over the eastern semicircle of the sheared system, has persisted for more the 12 hours. Recent ASCAT data indicated that the cyclone has maximum winds of 40 to 45 kt and a well-defined circulation. Based on these data, advisories are being initiated on Tropical Storm Claudette, the third tropical storm of the 2015 Atlantic hurricane season.
As of the 5:00 P.M. Advisory from the NHC in Miami, the following was available on CLAUDETTE:
5:00 PM AST Mon Jul 13
Location: 38.1°N 66.9°W
Moving: NE at 17 mph
Min pressure: 1004 mb/29.65 in
Max sustained: 50 mph
CLAUDETTE is now undergoing 30 knots of wind shear, which has allowed the LLC to become exposed, and is noted in the satellite loop imagery. Based on this, and being over much cooler waters, which are cooler than what is needed to sustain a tropical system, I expect CLAUDETTE to begin weakening at a steady pace during the next 24-36 hours.
CLAUDETTE is mainly a hazard to shipping at the moment, but could affect the extreme eastern portion of Nova Scotia by late Tues/early Wed.
As I stated, one is probably wondering what happened. Based on my analysis of various parameters, my take is, having looked at the forecast wind shear maps from earlier today, upper level winds did in fact relax to about only 10 – 15 knots right over the area. This allowed for whatever convection there was, to be much more focused near or closer toward the LLC. Albeit the SST’s in the area where development occurred are not warm enough to sustain a tropical cyclone, or sub-tropical cyclone for that matter, the cyclone early this morning, until around the noon time hour, did still have frontal characteristics, and was under baroclinic forcing, in which part of the energy is derived from strong differences in temperature gradient. Baroclinic Zone defined:
A region in which a temperature gradient exists on a constant pressure surface, which occurs in both strengthening and weakening weather systems. Wind shear is characteristic of a baroclinic zone.
This is most likely what stared the process of strengthening. Now, up until about the time NHC issued the Special Discussion, the frontal boundary was still associated with INVEST 92L, and was noted on the 12Z TAFB Surface analysis map. Between that time and the update of the 18Z map, NHC indicated that the frontal characteristics had dissipated. This would in fact lead toward tropical cyclone status. I was a little skeptical of this, as the frontal overlays of the satellite loop imagery indicate the storm still attached to the frontal boundary, but these do have a tendency to be misleading. Thus based on analysis of the 18Z TAFB Surface Analysis, I must side with the NHC. I as a forecaster only seeing what I had in front of me earlier this evening, would have been hesitant to name the system.
However, based on further analysis, in my opinion as a forecaster, I believe I would have gone sub-tropical in nature on this, as of earlier today, AMSU Data did not present a warm core system. The red line represents where the approximate center of the cyclone is located. Temperatures are noted to be -1.0C to 0.0C. For a system to be warm core, the center has to be warmer, relative to the surrounding atmosphere. Of course, this was from early this a.m., and warming could have occurred in the core, but I find it a little hard that sst’s on the order of only 22C would warm a core sufficiently, unless during the transition process, her core trapped warmer air in what we term as a warm seclusion. Personally, as a forecaster, I would have gone with sub-tropical classification…but that’s just me. As I learned from the NHC at the 2010 conference, the final call lies with the forecaster on duty.
Based on forecast steering maps, and the current Dynamic Model track guidance, I agree with the NHC forecast track.
I will try to have another update, or Tropical Outlook Wed. and Thur., time permitting.
Elsewhere, Tropical Storm formation is not expected during the next 7 days.
Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST / SEVERE WEATHER SPECIALIST MEMBER WEST CENTRAL FLORIDA AMS