Moderators StretchCT Posted September 26, 2024 Moderators Posted September 26, 2024 (edited) The hash came out yesterday morning and by 11pm it was a tropical storm. Tropical Storm Isaac Advisory Number 1 NWS National Hurricane Center Miami FL AL102024 1100 PM AST Wed Sep 25 2024 ...NEW TROPICAL STORM FORMS IN THE OPEN CENTRAL SUBTROPICAL ATLANTIC... SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION ----------------------------------------------- LOCATION...37.1N 54.1W ABOUT 1480 MI...2380 KM W OF THE AZORES ABOUT 690 MI...1115 KM ENE OF BERMUDA MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H PRESENT MOVEMENT...E OR 85 DEGREES AT 12 MPH...19 KM/H MINIMUM CENTRAL PRESSURE...997 MB...29.44 INCHES Tropical Storm Isaac Discussion Number 1 NWS National Hurricane Center Miami FL AL102024 1100 PM AST Wed Sep 25 2024 The non-tropical area of low pressure we have been monitoring to the northeast of Bermuda over the last day or so has become significantly better organized today, with deep central convection forming and now wrapping around a small surface circulation. While the system had previously been attached to an occluded frontal boundary to its northwest, recently received scatterometer data now shows that the circulation has fully detached form this boundary, and is producing winds of 40-45 kt in a small circular area embedded within the organizing convection. These structural changes indicate the the system has undergone and has completed tropical transition. Thus, the system is now being designated Tropical Storm Isaac this advisory, and the initial intensity is set to 45 kt based on the earlier scatterometer data. Isaac is moving just north of due east at 85/10 kt. This motion should continue with a gentle turn more east-northeastward over the next several days as the system is steered primarily by mid-level ridging present to its south. However, there does not appear to be a mid-latitude trough early on to help the storm to accelerate much over the next few days. The initial NHC track forecast is in good agreement with the simple and corrected consensus aids TCVN and HCCA. While Isaac is traversing only marginally warm waters, it is also still embedded within the base of an upper-level trough which has reduced tropospheric stability due to colder upper-level temperatures. This is partially why Isaac has been able to develop organized deep convection this evening. The shear is not anticipated to increase much over the next couple of days, which could allow for some gradual intensification. The NHC intensity forecast is in good agreement the with HCCA and ECMWF forecasts and shows a peak intensity of 60 kt in 48 h, followed by gradual weakening after 72 h as sea-surface temperatures cool further and shear begins to increase more markedly. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 37.1N 54.1W 45 KT 50 MPH 12H 26/1200Z 37.1N 52.3W 50 KT 60 MPH 24H 27/0000Z 37.3N 49.8W 50 KT 60 MPH 36H 27/1200Z 37.9N 46.8W 55 KT 65 MPH 48H 28/0000Z 38.8N 43.2W 60 KT 70 MPH 60H 28/1200Z 40.1N 39.5W 60 KT 70 MPH 72H 29/0000Z 41.4N 35.8W 60 KT 70 MPH 96H 30/0000Z 42.7N 29.4W 55 KT 65 MPH 120H 01/0000Z 42.5N 21.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Papin Edited September 30, 2024 by StretchCT 1
Moderators StretchCT Posted September 26, 2024 Author Moderators Posted September 26, 2024 Forecast to become a hurricane now. Spoiler Tropical Storm Isaac Discussion Number 2 NWS National Hurricane Center Miami FL AL102024 500 AM AST Thu Sep 26 2024 Isaac's structure on satellite looks fairly healthy for a high-latitude tropical cyclone. There are plenty of curved banding features rotating around the estimated center on IR satellite, matched by a recent AMSR2 microwave pass also showing convective banding. While the cloud top temperatures are not that cold, only -50 to -60 C, that is rather typical for a tropical cyclone along the axis of an upper-level trough with a depressed tropopause. Based on the earlier scatterometer wind data, plus a DMINT estimate from the AMSR2 pass of 46 kt, the initial intensity is held at 45 kt this advisory. The tropical storm is continuing eastward this morning at 90/10 kt. This general motion, albeit with a gradual turn more east-northeastward is expected over the next several days as Isaac slowly accelerates under the influence of mid-level ridging to the southeast of the storm. The track guidance is in pretty good agreement in the short-term. However, differences primarily in the along-track direction begin to be evident beyond 48 h, which could ultimately play a role in more notable across-track differences shown between the GFS and ECMWF solutions by early next week. For now, the NHC track forecast is very similar to the previous track forecast, and favors a solution very similar to the HFIP corrected consensus approach (HCCA) and ECMWF track. Given the storm's healthy current structure, there is an opportunity for it to intensify over the next couple of days. During this time span, sea-surface temperatures (SSTs) hover between 26-27 C, colder than normal upper-level temperatures should aid tropospheric instability, and vertical wind shear is forecast to remain in the 15-20 kt range, in the same direction as the storm motion. The simulated IR imagery from the latest ECMWF and GFS runs also show Isaac attempting to clear out an eye occasionally in the 36-60 h period. These signals suggest that Isaac could become a hurricane, and that is now explicitly reflected in the latest NHC forecast, which is very close to the latest HCCA consensus aid. After 60 h, shear increases markedly as SSTs also decrease, which should lead to weakening, and Isaac is forecast to become post-tropical sometime near the end of the forecast as it passes by to the north of the Azores. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 37.1N 52.8W 45 KT 50 MPH 12H 26/1800Z 37.2N 50.9W 50 KT 60 MPH 24H 27/0600Z 37.6N 48.1W 55 KT 65 MPH 36H 27/1800Z 38.3N 44.9W 60 KT 70 MPH 48H 28/0600Z 39.4N 41.2W 65 KT 75 MPH 60H 28/1800Z 40.5N 37.9W 65 KT 75 MPH 72H 29/0600Z 41.8N 34.0W 60 KT 70 MPH 96H 30/0600Z 43.0N 27.2W 55 KT 65 MPH 120H 01/0600Z 43.4N 19.4W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Papin NNNN FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 37.1N 52.8W 45 KT 50 MPH 12H 26/1800Z 37.2N 50.9W 50 KT 60 MPH 24H 27/0600Z 37.6N 48.1W 55 KT 65 MPH 36H 27/1800Z 38.3N 44.9W 60 KT 70 MPH 48H 28/0600Z 39.4N 41.2W 65 KT 75 MPH 60H 28/1800Z 40.5N 37.9W 65 KT 75 MPH 72H 29/0600Z 41.8N 34.0W 60 KT 70 MPH 96H 30/0600Z 43.0N 27.2W 55 KT 65 MPH 120H 01/0600Z 43.4N 19.4W 50 KT 60 MPH...POST-TROP/EXTRATROP
Moderators StretchCT Posted September 27, 2024 Author Moderators Posted September 27, 2024 Isaac getting a bump up at 11pm. 11:00 PM AST Thu Sep 26 Location: 37.1°N 49.8°W Moving: E at 12 mph Min pressure: 992 mb Max sustained: 65 mph\ FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 37.1N 49.8W 55 KT 65 MPH 12H 27/1200Z 37.1N 47.6W 65 KT 75 MPH 24H 28/0000Z 38.1N 44.1W 70 KT 80 MPH 36H 28/1200Z 39.5N 40.5W 70 KT 80 MPH 48H 29/0000Z 41.1N 37.9W 65 KT 75 MPH 60H 29/1200Z 42.6N 36.4W 65 KT 75 MPH 72H 30/0000Z 43.7N 35.1W 60 KT 70 MPH 96H 01/0000Z 46.0N 30.4W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 02/0000Z 50.0N 26.0W 40 KT 45 MPH...POST-TROP/EXTRATROP
Moderators StretchCT Posted September 27, 2024 Author Moderators Posted September 27, 2024 Hurricane Isaac Discussion Number 7 NWS National Hurricane Center Miami FL AL102024 1100 AM AST Fri Sep 27 2024 Isaac is holding steady this morning. Geostationary satellite data has shown consistent periodic bursts of convection wrapping around a small eye. Subjective and objective Dvorak estimates range widely from 35 kt to 73 kt and the initial intensity is held at 65 kt for this advisory, closest to the SAB classification. The hurricane is moving eastward at 12 kt. Isaac is moving along the northern periphery of a mid-level ridge and should gradually turn to the east-northeast over the next couple of days. Models are more in agreement this cycle and show a more northeastward turn on days 4 and 5 as Isaac interacts with an upper-level trough located to its east. The latest track forecast is similar to the previous forecast through 72 h and slightly to the north at forecast periods beyond. Isaac could still strengthen further over the next day or so. While the vertical wind shear is expected to be strong-to-moderate, the upper-level divergence is forecast to increase and sea surface temperature should be relatively sufficient. Beyond a day or so, oceanic and environmental conditions become less conducive, which should begin to weaken Isaac by Saturday night or Sunday. The official intensity forecast is very similar to previous advisory, with a peak intensity of 75 kt by Saturday and the cyclone becoming extratropical by early next week. However, global models show the system losing its deep convection by Monday, and the official forecast now predicts Isaac becoming a post-tropical cyclone at that point. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 37.4N 46.8W 65 KT 75 MPH 12H 28/0000Z 38.1N 44.2W 70 KT 80 MPH 24H 28/1200Z 39.4N 40.9W 75 KT 85 MPH 36H 29/0000Z 41.0N 38.4W 75 KT 85 MPH 48H 29/1200Z 42.4N 36.6W 70 KT 80 MPH 60H 30/0000Z 43.7N 35.1W 60 KT 70 MPH 72H 30/1200Z 44.8N 33.0W 55 KT 65 MPH...POST-TROPICAL 96H 01/1200Z 48.0N 29.6W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 02/1200Z 52.1N 25.0W 35 KT 40 MPH...POST-TROP/EXTRATROP
Moderators StretchCT Posted September 27, 2024 Author Moderators Posted September 27, 2024 5pm disco Hurricane Isaac Discussion Number 8 NWS National Hurricane Center Miami FL AL102024 500 PM AST Fri Sep 27 2024 Isaac's satellite presentation has improved since this morning. A small ragged eye can be seen on infrared imagery with cooler cloud tops surrounding it. An AMSR2 microwave pass from earlier today showed the mid- and low-level centers co-located with a primary band in the northwestern quadrant. Both the SAB and TAFB subjective Dvorak classifications suggested that Isaac's intensity has increased. Objective guidance aids are also suggesting the same. Taking all of these into consideration, the intensity has been increased to 75 kt. The hurricane is moving eastward at 14 kt. Isaac is moving in the mid-latitude zonal flow and will gradual turn to the east-northeast later today. In about a day or so, Isaac will begin interacting with an upper-level trough to its east and turn more northeastward and slow down. The latest track forecast is very similar to the previous forecast, however, the day four and five track positions were adjusted westward as the model guidance has been shifting in this direction. Isaac is close to its peak intensity as the window for strengthening is ending soon. By Saturday, it will move over cooler waters, into an area of strong vertical wind shear, and a dry mid-level airmass. The peak intensity has been adjusted upward to 80 kt because of the recent strengthening. On Saturday, Isaac is expect to gradually weaken and this trend will continue for the reminder of the forecast period. Simulated satellite imagery from the global models show Isaac losing its deep convection by Monday and the official forecast now predicts the hurricane to become a post-tropical cyclone by 60 h. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 37.8N 45.3W 75 KT 85 MPH 12H 28/0600Z 38.8N 42.7W 80 KT 90 MPH 24H 28/1800Z 40.3N 39.8W 75 KT 85 MPH 36H 29/0600Z 41.8N 37.9W 70 KT 80 MPH 48H 29/1800Z 43.1N 36.3W 65 KT 75 MPH 60H 30/0600Z 44.4N 34.5W 60 KT 70 MPH...POST-TROPICAL 72H 30/1800Z 45.7N 32.7W 50 KT 60 MPH...POST-TROPICAL 96H 01/1800Z 50.1N 29.9W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 02/1800Z 52.9N 27.3W 35 KT 40 MPH...POST-TROP/EXTRATROP $$
Moderators StretchCT Posted September 27, 2024 Author Moderators Posted September 27, 2024 5:00 PM AST Fri Sep 27 Location: 37.8°N 45.3°W Moving: E at 16 mph Min pressure: 976 mb Max sustained: 85 mph
Moderators StretchCT Posted September 28, 2024 Author Moderators Posted September 28, 2024 Isaac is overperforming despite moderate shear and marginal water temps. It's crazy that 26c water is that far north. But as it's now crossed into sub 26c water and the shear is picking up, it's likely peaked. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 40.2N 39.7W 90 KT 105 MPH 12H 29/0000Z 41.4N 37.8W 85 KT 100 MPH 24H 29/1200Z 42.9N 36.1W 75 KT 85 MPH 36H 30/0000Z 44.0N 33.9W 65 KT 75 MPH 48H 30/1200Z 45.4N 31.5W 55 KT 65 MPH...POST-TROPICAL 60H 01/0000Z 47.1N 29.4W 45 KT 50 MPH...POST-TROPICAL 72H 01/1200Z 49.6N 28.7W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 02/1200Z 53.5N 28.1W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 03/1200Z 56.6N 25.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 2
Moderators StretchCT Posted September 28, 2024 Author Moderators Posted September 28, 2024 Isaac starting to weaken 9:00 PM GMT Sat Sep 28 Location: 41.3°N 38.4°W Moving: NE at 18 mph Min pressure: 968 mb Max sustained: 100 mph
Moderators StretchCT Posted September 29, 2024 Author Moderators Posted September 29, 2024 3:00 AM GMT Sun Sep 29 Location: 42.1°N 37.6°W Moving: NE at 14 mph Min pressure: 972 mb Max sustained: 80 mph
Moderators StretchCT Posted September 29, 2024 Author Moderators Posted September 29, 2024 (edited) Edited September 29, 2024 by StretchCT
Moderators StretchCT Posted September 30, 2024 Author Moderators Posted September 30, 2024 Was surprised that this was still tropical. Spoiler 900 AM GMT Mon Sep 30 2024 Isaac continues to show signs of transitioning into an extratropical cyclone. The central convection has mostly dissipated, and the system is taking on more of a frontal appearance, with a zonally-oriented cloud and rain shield over the cyclone's northern semicircle. The current intensity is kept at 55 kt in accordance with a Dvorak estimate from TAFB, although this is somewhat uncertain since Isaac no longer appears to be a true tropical cyclone. The cyclone continues to move east-northeastward or at about 060/13 kt within a southern branch of the mid-latitude westerlies. Isaac is expected to turn toward the northeast during the next couple of days as it approaches a shortwave ridge just west of the British Isles. The official track forecast has been nudged only slightly eastward in the 2-3 day time frame, towards the latest corrected dynamical model consensus. Isaac is moving over cool waters and should complete its extratropical transition today. The global models suggest that the system will gradually weaken during the next few days as it becomes absorbed within a larger low over the North Atlantic. The official intensity forecast is similar to the previous NHC prediction. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 44.7N 31.3W 55 KT 65 MPH 12H 30/1800Z 45.8N 28.1W 50 KT 60 MPH...POST-TROP/EXTRATROP 24H 01/0600Z 47.4N 25.1W 45 KT 50 MPH...POST-TROP/EXTRATROP 36H 01/1800Z 49.4N 23.3W 40 KT 45 MPH...POST-TROP/EXTRATROP 48H 02/0600Z 51.3N 22.3W 40 KT 45 MPH...POST-TROP/EXTRATROP 60H 02/1800Z 53.0N 21.2W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 03/0600Z 54.5N 20.0W 30 KT 35 MPH...POST-TROP/EXTRATROP 96H 04/0600Z...DISSIPATED
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