I'm not sure what the decision making on that is sometimes.
93L is denoted with a low on surface analysis:
http://www.opc.ncep.noaa.gov/UA/Atl_Tropics.gif
From: http://www.nhc.noaa.gov/marine/
Or surface analysis for 18Z from link from Tropical Weather Discussion:
http://www.nhc.noaa.gov/tafb/USA_18Z.gif
But in the best track database it is a 1014mb disturbance at 8pm EDT Thursday. (You can view raw best track data from the NHC in the HurricaneCity model system)
94L is a wave on surface analysis. In the best track database it is also a wave with a pressure of 1010mb.
Neither are designated as lows in the best track database.
What an invest is, is important to note:
"Invest:
A weather system for which a tropical cyclone forecast center (NHC, CPHC, or JTWC) is interested in collecting specialized data sets (e.g., microwave imagery) and/or running model guidance. Once a system has been designated as an invest, data collection and processing is initiated on a number of government and academic web sites, including the Naval Research Laboratory (NRL) and the University of Wisconsin Cooperative Institute for Meteorological Satellite Studies (UW-CIMSS). The designation of a system as an invest does not correspond to any particular likelihood of development of the system into a tropical cyclone; operational products such as the Tropical Weather Outlook or the JTWC/TCFA should be consulted for this purpose."
From:
http://www.nhc.noaa.gov/aboutgloss.shtml#invest
So if the NHC finds it interesting, I guess they run models. Since an invest's models are run from a center point, unless you have a circulation or some kind of center of low pressure, I don't know how you would have an invest. I don't know how they find the center of a wave. Maybe their best estimation.
For 94L, this from the discussion:
"A tropical wave is moving across the east Tropical Atlantic with
axis extending from 18N33W to 06N33W, moving west near 20 kt
over the past 24 hours. The wave is embedded within a surge of
moisture as seen on the Total Precipitable Water Imagery.
Scatterometer data depicts a weak low-level cyclonic circulation
trying to develop in the vicinity of this wave with center along
35W. Scattered moderate convection is observed from 05N-16N
between 28W-40W."
So until that happened, maybe they did not declare the invest? I see the ASCAT pass that likely resulted in that.
http://manati.star.nesdis.noaa.gov/ascat_images/cur_25km_METB/zooms/WMBas112.png
From ASCAT-B:
http://manati.star.nesdis.noaa.gov/datasets/ASCATBData.php
At the moment shows the pass from 7:31pm EDT (23:31Z). The invest was started at 8pm EDT with a position of 10.9N 34.6W. Maybe they had not had that image yet and were working from an earlier ASCAT pass:
http://manati.star.nesdis.noaa.gov/ascat_images/cur_25km_META/zooms/WMBds112.png
Because the invest seems placed further east than I would have thought.
Raw best track data:
93L:
AL, 93, 2016090712, , BEST, 0, 150N, 515W, 25, 1010, DB, 0, , 0, 0, 0, 0, 1014, 150, 50, 0, 0, , 0, , 0, 0, INVEST, ,
AL, 93, 2016090718, , BEST, 0, 157N, 532W, 25, 1010, DB, 0, , 0, 0, 0, 0, 1014, 150, 50, 0, 0, , 0, , 0, 0, INVEST, ,
AL, 93, 2016090800, , BEST, 0, 163N, 549W, 25, 1010, DB, 0, , 0, 0, 0, 0, 1014, 150, 50, 0, 0, , 0, , 0, 0, INVEST, ,
AL, 93, 2016090806, , BEST, 0, 167N, 560W, 25, 1010, DB, 0, , 0, 0, 0, 0, 1014, 150, 50, 0, 0, , 0, , 0, 0, INVEST, ,
AL, 93, 2016090812, , BEST, 0, 172N, 570W, 25, 1009, DB, 0, , 0, 0, 0, 0, 1010, 150, 0, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 93, 2016090818, , BEST, 0, 177N, 585W, 20, 1014, DB, 0, , 0, 0, 0, 0, 1016, 150, 0, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 93, 2016090900, , BEST, 0, 179N, 600W, 20, 1014, DB, 34, NEQ, 0, 0, 0, 0, 1016, 150, 30, 0, 0, L, 0, , 0, 0, INVEST, S,
94L
AL, 94, 2016090806, , BEST, 0, 105N, 285W, 20, 1010, WV, 0, , 0, 0, 0, 0, 0, 0, 0, 0, 0, , 0, , 0, 0, GENESIS020, , 0, , 0, 0, 0, 0, genesis-num, 020,
AL, 94, 2016090812, , BEST, 0, 107N, 302W, 20, 1010, WV, 0, , 0, 0, 0, 0, 0, 0, 0, 0, 0, , 0, , 0, 0, GENESIS020, , 0, , 0, 0, 0, 0, genesis-num, 020,
AL, 94, 2016090818, , BEST, 0, 108N, 324W, 20, 1010, WV, 0, , 0, 0, 0, 0, 0, 0, 0, 0, 0, , 0, , 0, 0, GENESIS020, , 0, , 0, 0, 0, 0, genesis-num, 020,
AL, 94, 2016090900, , BEST, 0, 109N, 346W, 20, 1010, WV, 34, NEQ, 0, 0, 0, 0, 1011, 150, 50, 0, 0, L, 0, , 0, 0, INVEST, S, 0, , 0, 0, 0, 0, genesis-num, 020, SPAWNINVEST, al742016 to al942016,
The NHC was tracking 94L internally it seems, changing 74L to 94L.
Maybe the NHC also goes on model support. If no global models do anything, maybe they hold off on a public invest. I don't think there are very set rules on when they run an invest. |